prism3_function/

mutator.rs

/*******************************************************************************
 *
 *    Copyright (c) 2025.
 *    3-Prism Co. Ltd.
 *
 *    All rights reserved.
 *
 ******************************************************************************/
//! # Mutator Types
//!
//! Provides Java-like `Mutator` interface implementations for performing
//! operations that accept a single mutable input parameter and return no result.
//!
//! This module provides a unified `Mutator` trait and three concrete
//! implementations based on different ownership models:
//!
//! - **`BoxMutator<T>`**: Box-based single ownership implementation for
//!   one-time use scenarios and builder patterns
//! - **`ArcMutator<T>`**: Arc<Mutex<>>-based thread-safe shared ownership
//!   implementation for multi-threaded scenarios
//! - **`RcMutator<T>`**: Rc<RefCell<>>-based single-threaded shared
//!   ownership implementation with no lock overhead
//!
//! # Design Philosophy
//!
//! Unlike `Consumer` which observes values without modifying them (`FnMut(&T)`),
//! `Mutator` is designed to **modify input values** using `FnMut(&mut T)`.
//!
//! ## Mutator vs Consumer
//!
//! | Type | Input | Modifies Input? | Modifies Self? | Use Cases |
//! |------|-------|----------------|----------------|-----------|
//! | **Consumer** | `&T` | ❌ | ✅ | Observe, log, count, notify |
//! | **Mutator** | `&mut T` | ✅ | ✅ | Modify, transform, update |
//!
//! **Key Insight**: If you need to modify input values, use `Mutator`.
//! If you only need to observe or accumulate state, use `Consumer`.
//!
//! # Comparison Table
//!
//! | Feature          | BoxMutator | ArcMutator | RcMutator |
//! |------------------|------------|------------|-----------|
//! | Ownership        | Single     | Shared     | Shared    |
//! | Cloneable        | ❌         | ✅         | ✅        |
//! | Thread-Safe      | ❌         | ✅         | ❌        |
//! | Interior Mut.    | N/A        | Mutex      | RefCell   |
//! | `and_then` API   | `self`     | `&self`    | `&self`   |
//! | Lock Overhead    | None       | Yes        | None      |
//!
//! # Use Cases
//!
//! ## BoxMutator
//!
//! - One-time operations that don't require sharing
//! - Builder patterns where ownership naturally flows
//! - Simple scenarios with no reuse requirements
//!
//! ## ArcMutator
//!
//! - Multi-threaded shared operations
//! - Concurrent task processing (e.g., thread pools)
//! - Situations requiring the same mutator across threads
//!
//! ## RcMutator
//!
//! - Single-threaded operations with multiple uses
//! - Event handling in single-threaded UI frameworks
//! - Performance-critical single-threaded scenarios
//!
//! # Examples
//!
//! ## Basic Usage
//!
//! ```rust
//! use prism3_function::{BoxMutator, ArcMutator, RcMutator, Mutator};
//!
//! // BoxMutator: Single ownership, consumes self
//! let mut mutator = BoxMutator::new(|x: &mut i32| *x *= 2);
//! let mut value = 5;
//! mutator.mutate(&mut value);
//! assert_eq!(value, 10);
//!
//! // ArcMutator: Shared ownership, cloneable, thread-safe
//! let shared = ArcMutator::new(|x: &mut i32| *x *= 2);
//! let clone = shared.clone();
//! let mut value = 5;
//! let mut m = shared;
//! m.mutate(&mut value);
//! assert_eq!(value, 10);
//!
//! // RcMutator: Shared ownership, cloneable, single-threaded
//! let rc = RcMutator::new(|x: &mut i32| *x *= 2);
//! let clone = rc.clone();
//! let mut value = 5;
//! let mut m = rc;
//! m.mutate(&mut value);
//! assert_eq!(value, 10);
//! ```
//!
//! ## Method Chaining
//!
//! ```rust
//! use prism3_function::{Mutator, BoxMutator, ArcMutator};
//!
//! // BoxMutator: Consumes self
//! let mut chained = BoxMutator::new(|x: &mut i32| *x *= 2)
//!     .and_then(|x: &mut i32| *x += 10);
//! let mut value = 5;
//! chained.mutate(&mut value);
//! assert_eq!(value, 20); // (5 * 2) + 10
//!
//! // ArcMutator: Borrows &self, original still usable
//! let first = ArcMutator::new(|x: &mut i32| *x *= 2);
//! let second = ArcMutator::new(|x: &mut i32| *x += 10);
//! let combined = first.and_then(&second);
//! // first and second are still usable here
//! ```
//!
//! ## Working with Closures
//!
//! All closures automatically implement the `Mutator` trait:
//!
//! ```rust
//! use prism3_function::{Mutator, FnMutatorOps};
//!
//! // Closures can use .mutate() directly
//! let mut closure = |x: &mut i32| *x *= 2;
//! let mut value = 5;
//! closure.mutate(&mut value);
//! assert_eq!(value, 10);
//!
//! // Closures can be chained, returning BoxMutator
//! let mut chained = (|x: &mut i32| *x *= 2)
//!     .and_then(|x: &mut i32| *x += 10);
//! let mut value = 5;
//! chained.mutate(&mut value);
//! assert_eq!(value, 20);
//! ```
//!
//! ## Type Conversions
//!
//! ```rust
//! use prism3_function::Mutator;
//!
//! // Convert closure to concrete type
//! let closure = |x: &mut i32| *x *= 2;
//! let mut box_mutator = closure.into_box();
//!
//! let closure = |x: &mut i32| *x *= 2;
//! let mut rc_mutator = closure.into_rc();
//!
//! let closure = |x: &mut i32| *x *= 2;
//! let mut arc_mutator = closure.into_arc();
//! ```
//!
//! ## Conditional Execution
//!
//! All mutator types support conditional execution through the `when` method,
//! which returns a `ConditionalMutator`. You can optionally add an `or_else`
//! branch to create if-then-else logic:
//!
//! ```rust
//! use prism3_function::{Mutator, BoxMutator};
//!
//! // Simple conditional (if-then)
//! let mut conditional = BoxMutator::new(|x: &mut i32| *x *= 2)
//!     .when(|x: &i32| *x > 0);
//!
//! let mut positive = 5;
//! conditional.mutate(&mut positive);
//! assert_eq!(positive, 10); // Executed
//!
//! let mut negative = -5;
//! conditional.mutate(&mut negative);
//! assert_eq!(negative, -5); // Not executed
//!
//! // Conditional with else branch (if-then-else)
//! let mut branched = BoxMutator::new(|x: &mut i32| *x *= 2)
//!     .when(|x: &i32| *x > 0)
//!     .or_else(|x: &mut i32| *x -= 1);
//!
//! let mut positive = 5;
//! branched.mutate(&mut positive);
//! assert_eq!(positive, 10); // when branch
//!
//! let mut negative = -5;
//! branched.mutate(&mut negative);
//! assert_eq!(negative, -6); // or_else branch
//! ```
//!
//! # Author
//!
//! Haixing Hu

use std::cell::RefCell;
use std::rc::Rc;
use std::sync::{Arc, Mutex};

use crate::predicate::{ArcPredicate, BoxPredicate, Predicate, RcPredicate};

// ============================================================================
// 1. Mutator Trait - Unified Mutator Interface
// ============================================================================

/// Mutator trait - Unified mutator interface
///
/// Defines the core behavior of all mutator types. Performs operations that
/// accept a mutable reference and modify the input value (not just side effects).
///
/// This trait is automatically implemented by:
/// - All closures implementing `FnMut(&mut T)`
/// - `BoxMutator<T>`, `ArcMutator<T>`, and `RcMutator<T>`
///
/// # Design Rationale
///
/// The trait provides a unified abstraction over different ownership models,
/// allowing generic code to work with any mutator type. Type conversion
/// methods (`into_box`, `into_arc`, `into_rc`) enable flexible ownership
/// transitions based on usage requirements.
///
/// # Features
///
/// - **Unified Interface**: All mutator types share the same `mutate`
///   method signature
/// - **Automatic Implementation**: Closures automatically implement this
///   trait with zero overhead
/// - **Type Conversions**: Easy conversion between ownership models
/// - **Generic Programming**: Write functions that work with any mutator
///   type
///
/// # Examples
///
/// ## Generic Mutator Function
///
/// ```rust
/// use prism3_function::{Mutator, BoxMutator, ArcMutator};
///
/// fn apply_mutator<M: Mutator<i32>>(
///     mutator: &mut M,
///     value: i32
/// ) -> i32 {
///     let mut val = value;
///     mutator.mutate(&mut val);
///     val
/// }
///
/// // Works with any mutator type
/// let mut box_mut = BoxMutator::new(|x: &mut i32| *x *= 2);
/// assert_eq!(apply_mutator(&mut box_mut, 5), 10);
///
/// let mut arc_mut = ArcMutator::new(|x: &mut i32| *x *= 2);
/// assert_eq!(apply_mutator(&mut arc_mut, 5), 10);
///
/// let mut closure = |x: &mut i32| *x *= 2;
/// assert_eq!(apply_mutator(&mut closure, 5), 10);
/// ```
///
/// ## Type Conversion
///
/// ```rust
/// use prism3_function::Mutator;
///
/// let closure = |x: &mut i32| *x *= 2;
///
/// // Convert to different ownership models
/// let box_mutator = closure.into_box();
/// // let rc_mutator = closure.into_rc();  // closure moved
/// // let arc_mutator = closure.into_arc(); // closure moved
/// ```
///
/// # Author
///
/// Haixing Hu
pub trait Mutator<T> {
    /// Performs the mutation operation
    ///
    /// Executes an operation on the given mutable reference. The operation
    /// typically modifies the input value or produces side effects.
    ///
    /// # Parameters
    ///
    /// * `value` - A mutable reference to the value to be mutated
    ///
    /// # Examples
    ///
    /// ```rust
    /// use prism3_function::{Mutator, BoxMutator};
    ///
    /// let mut mutator = BoxMutator::new(|x: &mut i32| *x *= 2);
    /// let mut value = 5;
    /// mutator.mutate(&mut value);
    /// assert_eq!(value, 10);
    /// ```
    fn mutate(&mut self, value: &mut T);

    /// Convert this mutator into a `BoxMutator<T>`.
    ///
    /// This consuming conversion takes ownership of `self` and returns a
    /// boxed implementation that forwards calls to the original mutator.
    /// Types that can provide a more efficient conversion may override the
    /// default implementation.
    ///
    /// # Consumption
    ///
    /// This method consumes the mutator: the original value will no longer
    /// be available after the call. For cloneable mutators call `.clone()`
    /// before converting if you need to retain the original instance.
    ///
    /// # Returns
    ///
    /// A `BoxMutator<T>` that forwards to the original mutator.
    ///
    /// # Examples
    ///
    /// ```rust
    /// use prism3_function::Mutator;
    ///
    /// let closure = |x: &mut i32| *x *= 2;
    /// let mut boxed = closure.into_box();
    /// let mut value = 5;
    /// boxed.mutate(&mut value);
    /// assert_eq!(value, 10);
    /// ```
    fn into_box(mut self) -> BoxMutator<T>
    where
        Self: Sized + 'static,
        T: 'static,
    {
        BoxMutator::new(move |t| self.mutate(t))
    }

    /// Convert this mutator into an `RcMutator<T>`.
    ///
    /// This consuming conversion takes ownership of `self` and returns an
    /// `Rc`-backed mutator that forwards calls to the original. Override to
    /// provide a more direct or efficient conversion when available.
    ///
    /// # Consumption
    ///
    /// This method consumes the mutator. If you need to keep the original
    /// instance, clone it prior to calling this method.
    ///
    /// # Returns
    ///
    /// An `RcMutator<T>` forwarding to the original mutator.
    ///
    /// # Examples
    ///
    /// ```rust
    /// use prism3_function::Mutator;
    ///
    /// let closure = |x: &mut i32| *x *= 2;
    /// let mut rc = closure.into_rc();
    /// let mut value = 5;
    /// rc.mutate(&mut value);
    /// assert_eq!(value, 10);
    /// ```
    fn into_rc(mut self) -> RcMutator<T>
    where
        Self: Sized + 'static,
        T: 'static,
    {
        RcMutator::new(move |t| self.mutate(t))
    }

    /// Convert this mutator into an `ArcMutator<T>`.
    ///
    /// This consuming conversion takes ownership of `self` and returns an
    /// `Arc`-wrapped, thread-safe mutator. Types may override the default
    /// implementation to provide a more efficient conversion.
    ///
    /// # Consumption
    ///
    /// This method consumes the mutator. Clone the instance first if you
    /// need to retain the original for further use.
    ///
    /// # Returns
    ///
    /// An `ArcMutator<T>` that forwards to the original mutator.
    ///
    /// # Examples
    ///
    /// ```rust
    /// use prism3_function::Mutator;
    ///
    /// let closure = |x: &mut i32| *x *= 2;
    /// let mut arc = closure.into_arc();
    /// let mut value = 5;
    /// arc.mutate(&mut value);
    /// assert_eq!(value, 10);
    /// ```
    fn into_arc(mut self) -> ArcMutator<T>
    where
        Self: Sized + Send + 'static,
        T: Send + 'static,
    {
        ArcMutator::new(move |t| self.mutate(t))
    }

    /// Consume the mutator and return an `FnMut(&mut T)` closure.
    ///
    /// The returned closure forwards calls to the original mutator and is
    /// suitable for use with iterator adapters such as `for_each`.
    ///
    /// # Consumption
    ///
    /// This method consumes the mutator. The original instance will not be
    /// available after calling this method.
    ///
    /// # Returns
    ///
    /// A closure implementing `FnMut(&mut T)` which forwards to the
    /// original mutator.
    ///
    /// # Examples
    ///
    /// ```rust
    /// use prism3_function::{Mutator, BoxMutator};
    ///
    /// let mutator = BoxMutator::new(|x: &mut i32| *x *= 2);
    /// let mut values = vec![1, 2, 3, 4, 5];
    /// values.iter_mut().for_each(mutator.into_fn());
    /// assert_eq!(values, vec![2, 4, 6, 8, 10]);
    /// ```
    fn into_fn(mut self) -> impl FnMut(&mut T)
    where
        Self: Sized + 'static,
        T: 'static,
    {
        move |t| self.mutate(t)
    }

    /// Create a non-consuming `BoxMutator<T>` that forwards to `self`.
    ///
    /// The default implementation clones `self` (requires `Clone`) and
    /// returns a boxed mutator that calls the cloned instance. Override this
    /// method if a more efficient conversion exists.
    ///
    /// # Returns
    ///
    /// A `BoxMutator<T>` that forwards to a clone of `self`.
    fn to_box(&self) -> BoxMutator<T>
    where
        Self: Sized + Clone + 'static,
        T: 'static,
    {
        self.clone().into_box()
    }

    /// Create a non-consuming `RcMutator<T>` that forwards to `self`.
    ///
    /// The default implementation clones `self` (requires `Clone`) and
    /// returns an `Rc`-backed mutator that forwards calls to the clone.
    /// Override to provide a more direct or efficient conversion if needed.
    ///
    /// # Returns
    ///
    /// An `RcMutator<T>` that forwards to a clone of `self`.
    fn to_rc(&self) -> RcMutator<T>
    where
        Self: Sized + Clone + 'static,
        T: 'static,
    {
        self.clone().into_rc()
    }

    /// Create a non-consuming `ArcMutator<T>` that forwards to `self`.
    ///
    /// The default implementation clones `self` (requires `Clone + Send`) and
    /// returns an `Arc`-wrapped mutator that forwards calls to the clone.
    /// Override when a more efficient conversion is available.
    ///
    /// # Returns
    ///
    /// An `ArcMutator<T>` that forwards to a clone of `self`.
    fn to_arc(&self) -> ArcMutator<T>
    where
        Self: Sized + Clone + Send + 'static,
        T: Send + 'static,
    {
        self.clone().into_arc()
    }

    /// Create a boxed `FnMut(&mut T)` closure that forwards to `self`.
    ///
    /// The default implementation clones `self` (requires `Clone`) and
    /// returns a boxed closure that invokes the cloned instance. Override to
    /// provide a more efficient conversion when possible.
    ///
    /// # Returns
    ///
    /// A closure implementing `FnMut(&mut T)` which forwards to the
    /// original mutator.
    fn to_fn(&self) -> impl FnMut(&mut T)
    where
        Self: Sized + Clone + 'static,
        T: 'static,
    {
        self.clone().into_fn()
    }
}

// ============================================================================
// 2. Type Aliases
// ============================================================================

/// Type alias for Arc-wrapped mutable mutator function
type ArcMutMutatorFn<T> = Arc<Mutex<dyn FnMut(&mut T) + Send>>;

/// Type alias for Rc-wrapped mutable mutator function
type RcMutMutatorFn<T> = Rc<RefCell<dyn FnMut(&mut T)>>;

// ============================================================================
// 3. BoxMutator - Single Ownership Implementation
// ============================================================================

/// BoxMutator struct
///
/// A mutator implementation based on `Box<dyn FnMut(&mut T)>` for single
/// ownership scenarios. This is the simplest and most efficient mutator
/// type when sharing is not required.
///
/// # Features
///
/// - **Single Ownership**: Not cloneable, ownership moves on use
/// - **Zero Overhead**: No reference counting or locking
/// - **Mutable State**: Can modify captured environment via `FnMut`
/// - **Builder Pattern**: Method chaining consumes `self` naturally
/// - **Factory Methods**: Convenient constructors for common patterns
///
/// # Use Cases
///
/// Choose `BoxMutator` when:
/// - The mutator is used only once or in a linear flow
/// - Building pipelines where ownership naturally flows
/// - No need to share the mutator across contexts
/// - Performance is critical and no sharing overhead is acceptable
///
/// # Performance
///
/// `BoxMutator` has the best performance among the three mutator types:
/// - No reference counting overhead
/// - No lock acquisition or runtime borrow checking
/// - Direct function call through vtable
/// - Minimal memory footprint (single pointer)
///
/// # Examples
///
/// ```rust
/// use prism3_function::{Mutator, BoxMutator};
///
/// let mut mutator = BoxMutator::new(|x: &mut i32| *x *= 2);
/// let mut value = 5;
/// mutator.mutate(&mut value);
/// assert_eq!(value, 10);
/// ```
///
/// # Author
///
/// Haixing Hu
pub struct BoxMutator<T> {
    function: Box<dyn FnMut(&mut T)>,
}

impl<T> BoxMutator<T>
where
    T: 'static,
{
    /// Creates a new BoxMutator
    ///
    /// # Parameters
    ///
    /// * `f` - The closure to wrap
    ///
    /// # Returns
    ///
    /// Returns a new `BoxMutator<T>` instance
    ///
    /// # Examples
    ///
    /// ```rust
    /// use prism3_function::{Mutator, BoxMutator};
    ///
    /// let mut mutator = BoxMutator::new(|x: &mut i32| *x += 1);
    /// let mut value = 5;
    /// mutator.mutate(&mut value);
    /// assert_eq!(value, 6);
    /// ```
    pub fn new<F>(f: F) -> Self
    where
        F: FnMut(&mut T) + 'static,
    {
        BoxMutator {
            function: Box::new(f),
        }
    }

    /// Creates a no-op mutator
    ///
    /// Returns a mutator that performs no operation.
    ///
    /// # Returns
    ///
    /// Returns a no-op mutator
    ///
    /// # Examples
    ///
    /// ```rust
    /// use prism3_function::{Mutator, BoxMutator};
    ///
    /// let mut noop = BoxMutator::<i32>::noop();
    /// let mut value = 42;
    /// noop.mutate(&mut value);
    /// assert_eq!(value, 42); // Value unchanged
    /// ```
    pub fn noop() -> Self {
        BoxMutator::new(|_| {})
    }

    /// Chains another mutator in sequence
    ///
    /// Returns a new mutator that first executes the current operation, then
    /// executes the next operation. Consumes self.
    ///
    /// # Parameters
    ///
    /// * `next` - The mutator to execute after the current operation. **Note:
    ///   This parameter is passed by value and will transfer ownership.** If you
    ///   need to preserve the original mutator, clone it first (if it implements
    ///   `Clone`). Can be:
    ///   - A closure: `|x: &mut T|`
    ///   - A `BoxMutator<T>`
    ///   - An `ArcMutator<T>`
    ///   - An `RcMutator<T>`
    ///   - Any type implementing `Mutator<T>`
    ///
    /// # Returns
    ///
    /// Returns a new composed `BoxMutator<T>`
    ///
    /// # Examples
    ///
    /// ## Direct value passing (ownership transfer)
    ///
    /// ```rust
    /// use prism3_function::{Mutator, BoxMutator};
    ///
    /// let first = BoxMutator::new(|x: &mut i32| *x *= 2);
    /// let second = BoxMutator::new(|x: &mut i32| *x += 10);
    ///
    /// // second is moved here
    /// let mut chained = first.and_then(second);
    /// let mut value = 5;
    /// chained.mutate(&mut value);
    /// assert_eq!(value, 20);
    /// // second.mutate(&mut value); // Would not compile - moved
    /// ```
    ///
    /// ## Preserving original with clone
    ///
    /// ```rust
    /// use prism3_function::{Mutator, BoxMutator};
    ///
    /// let first = BoxMutator::new(|x: &mut i32| *x *= 2);
    /// let second = BoxMutator::new(|x: &mut i32| *x += 10);
    ///
    /// // Clone to preserve original
    /// let mut chained = first.and_then(second.clone());
    /// let mut value = 5;
    /// chained.mutate(&mut value);
    /// assert_eq!(value, 20);
    ///
    /// // Original still usable
    /// let mut value2 = 3;
    /// second.mutate(&mut value2);
    /// assert_eq!(value2, 13);
    /// ```
    pub fn and_then<C>(self, next: C) -> Self
    where
        C: Mutator<T> + 'static,
    {
        let mut first = self.function;
        let mut second = next.into_fn();
        BoxMutator::new(move |t| {
            (first)(t);
            second(t);
        })
    }

    /// Creates a conditional mutator
    ///
    /// Returns a mutator that only executes when a predicate is satisfied.
    ///
    /// # Parameters
    ///
    /// * `predicate` - The condition to check. **Note: This parameter is passed
    ///   by value and will transfer ownership.** If you need to preserve the
    ///   original predicate, clone it first (if it implements `Clone`).
    ///   Can be:
    ///   - A closure: `|x: &T| -> bool`
    ///   - A function pointer: `fn(&T) -> bool`
    ///   - A `BoxPredicate<T>`
    ///   - An `RcPredicate<T>`
    ///   - An `ArcPredicate<T>`
    ///   - Any type implementing `Predicate<T>`
    ///
    /// # Returns
    ///
    /// Returns `BoxConditionalMutator<T>`
    ///
    /// # Examples
    ///
    /// ## Using a closure
    ///
    /// ```rust
    /// use prism3_function::{Mutator, BoxMutator};
    ///
    /// let mutator = BoxMutator::new(|x: &mut i32| *x *= 2);
    /// let mut conditional = mutator.when(|x: &i32| *x > 0);
    ///
    /// let mut positive = 5;
    /// conditional.mutate(&mut positive);
    /// assert_eq!(positive, 10);
    ///
    /// let mut negative = -5;
    /// conditional.mutate(&mut negative);
    /// assert_eq!(negative, -5); // Unchanged
    /// ```
    ///
    /// ## Using BoxPredicate
    ///
    /// ```rust
    /// use prism3_function::{Mutator, BoxMutator};
    /// use prism3_function::predicate::{Predicate, BoxPredicate};
    ///
    /// let pred = BoxPredicate::new(|x: &i32| *x > 0);
    /// let mutator = BoxMutator::new(|x: &mut i32| *x *= 2);
    /// let mut conditional = mutator.when(pred);
    ///
    /// let mut value = 5;
    /// conditional.mutate(&mut value);
    /// assert_eq!(value, 10);
    /// ```
    ///
    /// ## Using composed predicate
    ///
    /// ```rust
    /// use prism3_function::{Mutator, BoxMutator};
    /// use prism3_function::predicate::{Predicate, FnPredicateOps};
    ///
    /// let pred = (|x: &i32| *x > 0).and(|x: &i32| x % 2 == 0);
    /// let mutator = BoxMutator::new(|x: &mut i32| *x *= 2);
    /// let mut conditional = mutator.when(pred);
    ///
    /// let mut value = 4;
    /// conditional.mutate(&mut value);
    /// assert_eq!(value, 8); // Positive and even
    ///
    /// let mut odd = 3;
    /// conditional.mutate(&mut odd);
    /// assert_eq!(odd, 3); // Positive but odd, unchanged
    /// ```
    pub fn when<P>(self, predicate: P) -> BoxConditionalMutator<T>
    where
        P: Predicate<T> + 'static,
    {
        BoxConditionalMutator {
            mutator: self,
            predicate: predicate.into_box(),
        }
    }
}

impl<T> Mutator<T> for BoxMutator<T> {
    fn mutate(&mut self, value: &mut T) {
        (self.function)(value)
    }

    fn into_box(self) -> BoxMutator<T>
    where
        T: 'static,
    {
        self
    }

    fn into_rc(self) -> RcMutator<T>
    where
        T: 'static,
    {
        let mut self_fn = self.function;
        RcMutator::new(move |t| self_fn(t))
    }

    // do NOT override Mutator::into_arc() because BoxMutator is not Send + Sync
    // and calling BoxMutator::into_arc() will cause a compile error

    fn into_fn(mut self) -> impl FnMut(&mut T)
    where
        Self: Sized + 'static,
        T: 'static,
    {
        move |t| (self.function)(t)
    }

    // do NOT override Mutator::to_xxx() because BoxMutator is not Clone
    // and calling BoxMutator::to_xxx() will cause a compile error
}

// ============================================================================
// 3. BoxConditionalMutator - Box-based Conditional Mutator
// ============================================================================

/// BoxConditionalMutator struct
///
/// A conditional mutator that only executes when a predicate is satisfied.
/// Uses `BoxMutator` and `BoxPredicate` for single ownership semantics.
///
/// This type is typically created by calling `BoxMutator::when()` and is
/// designed to work with the `or_else()` method to create if-then-else logic.
///
/// # Features
///
/// - **Single Ownership**: Not cloneable, consumes `self` on use
/// - **Conditional Execution**: Only mutates when predicate returns `true`
/// - **Chainable**: Can add `or_else` branch to create if-then-else logic
/// - **Implements Mutator**: Can be used anywhere a `Mutator` is expected
///
/// # Examples
///
/// ## Basic Conditional Execution
///
/// ```rust
/// use prism3_function::{Mutator, BoxMutator};
///
/// let mutator = BoxMutator::new(|x: &mut i32| *x *= 2);
/// let mut conditional = mutator.when(|x: &i32| *x > 0);
///
/// let mut positive = 5;
/// conditional.mutate(&mut positive);
/// assert_eq!(positive, 10); // Executed
///
/// let mut negative = -5;
/// conditional.mutate(&mut negative);
/// assert_eq!(negative, -5); // Not executed
/// ```
///
/// ## With or_else Branch
///
/// ```rust
/// use prism3_function::{Mutator, BoxMutator};
///
/// let mut mutator = BoxMutator::new(|x: &mut i32| *x *= 2)
///     .when(|x: &i32| *x > 0)
///     .or_else(|x: &mut i32| *x -= 1);
///
/// let mut positive = 5;
/// mutator.mutate(&mut positive);
/// assert_eq!(positive, 10); // when branch executed
///
/// let mut negative = -5;
/// mutator.mutate(&mut negative);
/// assert_eq!(negative, -6); // or_else branch executed
/// ```
///
/// # Author
///
/// Haixing Hu
pub struct BoxConditionalMutator<T> {
    mutator: BoxMutator<T>,
    predicate: BoxPredicate<T>,
}

impl<T> BoxConditionalMutator<T>
where
    T: 'static,
{
    /// Chains another mutator in sequence
    ///
    /// Combines the current conditional mutator with another mutator into a new
    /// mutator. The current conditional mutator executes first, followed by the
    /// next mutator.
    ///
    /// # Parameters
    ///
    /// * `next` - The next mutator to execute. **Note: This parameter is passed
    ///   by value and will transfer ownership.** If you need to preserve the
    ///   original mutator, clone it first (if it implements `Clone`). Can be:
    ///   - A closure: `|x: &mut T|`
    ///   - A `BoxMutator<T>`
    ///   - An `ArcMutator<T>`
    ///   - An `RcMutator<T>`
    ///   - Any type implementing `Mutator<T>`
    ///
    /// # Returns
    ///
    /// Returns a new `BoxMutator<T>`
    ///
    /// # Examples
    ///
    /// ## Direct value passing (ownership transfer)
    ///
    /// ```rust
    /// use prism3_function::{Mutator, BoxMutator};
    ///
    /// let cond1 = BoxMutator::new(|x: &mut i32| *x *= 2).when(|x: &i32| *x > 0);
    /// let cond2 = BoxMutator::new(|x: &mut i32| *x = 100).when(|x: &i32| *x > 100);
    ///
    /// // cond2 is moved here
    /// let mut chained = cond1.and_then(cond2);
    /// let mut value = 60;
    /// chained.mutate(&mut value);
    /// assert_eq!(value, 100); // First *2 = 120, then capped to 100
    /// // cond2.mutate(&mut value); // Would not compile - moved
    /// ```
    ///
    /// ## Preserving original with clone
    ///
    /// ```rust
    /// use prism3_function::{Mutator, BoxMutator};
    ///
    /// let cond1 = BoxMutator::new(|x: &mut i32| *x *= 2).when(|x: &i32| *x > 0);
    /// let cond2 = BoxMutator::new(|x: &mut i32| *x = 100).when(|x: &i32| *x > 100);
    ///
    /// // Clone to preserve original
    /// let mut chained = cond1.and_then(cond2.clone());
    /// let mut value = 60;
    /// chained.mutate(&mut value);
    /// assert_eq!(value, 100); // First *2 = 120, then capped to 100
    ///
    /// // Original still usable
    /// let mut value2 = 50;
    /// cond2.mutate(&mut value2);
    /// assert_eq!(value2, 100);
    /// ```
    pub fn and_then<C>(self, next: C) -> BoxMutator<T>
    where
        C: Mutator<T> + 'static,
    {
        let mut first = self;
        let mut second = next.into_fn();
        BoxMutator::new(move |t| {
            first.mutate(t);
            second(t);
        })
    }

    /// Adds an else branch
    ///
    /// Executes the original mutator when the condition is satisfied, otherwise
    /// executes else_mutator.
    ///
    /// # Parameters
    ///
    /// * `else_mutator` - The mutator for the else branch. **Note: This parameter
    ///   is passed by value and will transfer ownership.** If you need to preserve
    ///   the original mutator, clone it first (if it implements `Clone`). Can be:
    ///   - A closure: `|x: &mut T|`
    ///   - A `BoxMutator<T>`
    ///   - An `RcMutator<T>`
    ///   - An `ArcMutator<T>`
    ///   - Any type implementing `Mutator<T>`
    ///
    /// # Returns
    ///
    /// Returns the composed `BoxMutator<T>`
    ///
    /// # Examples
    ///
    /// ## Using a closure (recommended)
    ///
    /// ```rust
    /// use prism3_function::{Mutator, BoxMutator};
    ///
    /// let mut mutator = BoxMutator::new(|x: &mut i32| *x *= 2)
    ///     .when(|x: &i32| *x > 0)
    ///     .or_else(|x: &mut i32| *x -= 1);
    ///
    /// let mut positive = 5;
    /// mutator.mutate(&mut positive);
    /// assert_eq!(positive, 10); // Condition satisfied, execute *2
    ///
    /// let mut negative = -5;
    /// mutator.mutate(&mut negative);
    /// assert_eq!(negative, -6); // Condition not satisfied, execute -1
    /// ```
    pub fn or_else<C>(self, else_mutator: C) -> BoxMutator<T>
    where
        C: Mutator<T> + 'static,
    {
        let pred = self.predicate;
        let mut then_mut = self.mutator;
        let mut else_mut = else_mutator;
        BoxMutator::new(move |t| {
            if pred.test(t) {
                then_mut.mutate(t);
            } else {
                else_mut.mutate(t);
            }
        })
    }
}

impl<T> Mutator<T> for BoxConditionalMutator<T>
where
    T: 'static,
{
    fn mutate(&mut self, value: &mut T) {
        if self.predicate.test(value) {
            self.mutator.mutate(value);
        }
    }

    fn into_box(self) -> BoxMutator<T> {
        let pred = self.predicate;
        let mut mutator = self.mutator;
        BoxMutator::new(move |t| {
            if pred.test(t) {
                mutator.mutate(t);
            }
        })
    }

    fn into_rc(self) -> RcMutator<T> {
        let pred = self.predicate.into_rc();
        let mutator = self.mutator.into_rc();
        let mut mutator_fn = mutator;
        RcMutator::new(move |t| {
            if pred.test(t) {
                mutator_fn.mutate(t);
            }
        })
    }

    // do NOT override Mutator::into_arc() because BoxConditionalMutator is not Send + Sync
    // and calling BoxConditionalMutator::into_arc() will cause a compile error

    fn into_fn(self) -> impl FnMut(&mut T) {
        let pred = self.predicate;
        let mut mutator = self.mutator;
        move |t: &mut T| {
            if pred.test(t) {
                mutator.mutate(t);
            }
        }
    }

    // do NOT override Mutator::to_xxx() because BoxConditionalMutator is not Clone
    // and calling BoxConditionalMutator::to_xxx() will cause a compile error
}

// ============================================================================
// 4. RcMutator - Single-Threaded Shared Ownership Implementation
// ============================================================================

/// RcMutator struct
///
/// A mutator implementation based on `Rc<RefCell<dyn FnMut(&mut T)>>` for
/// single-threaded shared ownership scenarios. This type allows multiple
/// references to the same mutator without the overhead of thread safety.
///
/// # Features
///
/// - **Shared Ownership**: Cloneable via `Rc`, multiple owners allowed
/// - **Single-Threaded**: Not thread-safe, cannot be sent across threads
/// - **Interior Mutability**: Uses `RefCell` for runtime borrow checking
/// - **Mutable State**: Can modify captured environment via `FnMut`
/// - **Chainable**: Method chaining via `&self` (non-consuming)
/// - **Performance**: More efficient than `ArcMutator` (no locking)
///
/// # Use Cases
///
/// Choose `RcMutator` when:
/// - The mutator needs to be shared within a single thread
/// - Thread safety is not required
/// - Performance is important (avoiding lock overhead)
///
/// # Examples
///
/// ```rust
/// use prism3_function::{Mutator, RcMutator};
///
/// let mutator = RcMutator::new(|x: &mut i32| *x *= 2);
/// let clone = mutator.clone();
///
/// let mut value = 5;
/// let mut m = mutator;
/// m.mutate(&mut value);
/// assert_eq!(value, 10);
/// ```
///
/// # Author
///
/// Haixing Hu
pub struct RcMutator<T> {
    function: RcMutMutatorFn<T>,
}

impl<T> RcMutator<T>
where
    T: 'static,
{
    /// Creates a new RcMutator
    ///
    /// # Parameters
    ///
    /// * `f` - The closure to wrap
    ///
    /// # Returns
    ///
    /// Returns a new `RcMutator<T>` instance
    ///
    /// # Examples
    ///
    /// ```rust
    /// use prism3_function::{Mutator, RcMutator};
    ///
    /// let mutator = RcMutator::new(|x: &mut i32| *x += 1);
    /// let mut value = 5;
    /// let mut m = mutator;
    /// m.mutate(&mut value);
    /// assert_eq!(value, 6);
    /// ```
    pub fn new<F>(f: F) -> Self
    where
        F: FnMut(&mut T) + 'static,
    {
        RcMutator {
            function: Rc::new(RefCell::new(f)),
        }
    }

    /// Creates a no-op mutator
    ///
    /// Returns a mutator that performs no operation.
    ///
    /// # Returns
    ///
    /// Returns a no-op mutator
    ///
    /// # Examples
    ///
    /// ```rust
    /// use prism3_function::{Mutator, RcMutator};
    ///
    /// let noop = RcMutator::<i32>::noop();
    /// let mut value = 42;
    /// let mut m = noop;
    /// m.mutate(&mut value);
    /// assert_eq!(value, 42); // Value unchanged
    /// ```
    pub fn noop() -> Self {
        RcMutator::new(|_| {})
    }

    /// Chains another RcMutator in sequence
    ///
    /// Returns a new mutator that first executes the current operation, then
    /// executes the next operation. Borrows &self, does not consume the
    /// original mutator.
    ///
    /// # Parameters
    ///
    /// * `next` - The mutator to execute after the current operation
    ///
    /// # Returns
    ///
    /// Returns a new composed `RcMutator<T>`
    ///
    /// # Examples
    ///
    /// ```rust
    /// use prism3_function::{Mutator, RcMutator};
    ///
    /// let first = RcMutator::new(|x: &mut i32| *x *= 2);
    /// let second = RcMutator::new(|x: &mut i32| *x += 10);
    ///
    /// let chained = first.and_then(&second);
    ///
    /// // first and second are still usable
    /// let mut value = 5;
    /// let mut m = chained;
    /// m.mutate(&mut value);
    /// assert_eq!(value, 20); // (5 * 2) + 10
    /// ```
    pub fn and_then(&self, next: &RcMutator<T>) -> RcMutator<T> {
        let first = self.function.clone();
        let second = next.function.clone();
        RcMutator::new(move |t: &mut T| {
            (first.borrow_mut())(t);
            (second.borrow_mut())(t);
        })
    }

    /// Creates a conditional mutator (single-threaded shared version)
    ///
    /// Returns a mutator that only executes when a predicate is satisfied.
    ///
    /// # Parameters
    ///
    /// * `predicate` - The condition to check. **Note: This parameter is passed
    ///   by value and will transfer ownership.** If you need to preserve the
    ///   original predicate, clone it first (if it implements `Clone`). Can be:
    ///   - A closure: `|x: &T| -> bool`
    ///   - A function pointer: `fn(&T) -> bool`
    ///   - An `RcPredicate<T>`
    ///   - A `BoxPredicate<T>`
    ///   - Any type implementing `Predicate<T>`
    ///
    /// # Returns
    ///
    /// Returns `RcConditionalMutator<T>`
    ///
    /// # Examples
    ///
    /// ```rust
    /// use prism3_function::{Mutator, RcMutator};
    ///
    /// let mutator = RcMutator::new(|x: &mut i32| *x *= 2);
    /// let conditional = mutator.when(|x: &i32| *x > 0);
    ///
    /// let conditional_clone = conditional.clone();
    ///
    /// let mut positive = 5;
    /// let mut m = conditional;
    /// m.mutate(&mut positive);
    /// assert_eq!(positive, 10);
    /// ```
    pub fn when<P>(&self, predicate: P) -> RcConditionalMutator<T>
    where
        P: Predicate<T> + 'static,
    {
        RcConditionalMutator {
            mutator: self.clone(),
            predicate: predicate.into_rc(),
        }
    }
}

impl<T> Mutator<T> for RcMutator<T> {
    fn mutate(&mut self, value: &mut T) {
        (self.function.borrow_mut())(value)
    }

    fn into_box(self) -> BoxMutator<T>
    where
        T: 'static,
    {
        BoxMutator::new(move |t| self.function.borrow_mut()(t))
    }

    fn into_rc(self) -> RcMutator<T>
    where
        T: 'static,
    {
        self
    }

    // do NOT override Mutator::into_arc() because RcMutator is not Send + Sync
    // and calling RcMutator::into_arc() will cause a compile error

    fn into_fn(self) -> impl FnMut(&mut T)
    where
        Self: Sized + 'static,
        T: 'static,
    {
        move |t| self.function.borrow_mut()(t)
    }

    fn to_box(&self) -> BoxMutator<T>
    where
        Self: Sized + 'static,
        T: 'static,
    {
        let self_fn = self.function.clone();
        BoxMutator::new(move |t| self_fn.borrow_mut()(t))
    }

    fn to_rc(&self) -> RcMutator<T>
    where
        Self: Sized + 'static,
        T: 'static,
    {
        self.clone()
    }

    // do NOT override Mutator::to_arc() because RcMutator is not Send + Sync
    // and calling RcMutator::to_arc() will cause a compile error

    fn to_fn(&self) -> impl FnMut(&mut T)
    where
        Self: Sized + 'static,
        T: 'static,
    {
        let self_fn = self.function.clone();
        move |t| self_fn.borrow_mut()(t)
    }
}

impl<T> Clone for RcMutator<T> {
    /// Clones the RcMutator
    ///
    /// Creates a new RcMutator that shares the underlying function with the
    /// original instance.
    fn clone(&self) -> Self {
        RcMutator {
            function: self.function.clone(),
        }
    }
}

// ============================================================================
// 5. RcConditionalMutator - Rc-based Conditional Mutator
// ============================================================================

/// RcConditionalMutator struct
///
/// A single-threaded conditional mutator that only executes when a predicate is
/// satisfied. Uses `RcMutator` and `RcPredicate` for shared ownership within a
/// single thread.
///
/// This type is typically created by calling `RcMutator::when()` and is
/// designed to work with the `or_else()` method to create if-then-else logic.
///
/// # Features
///
/// - **Shared Ownership**: Cloneable via `Rc`, multiple owners allowed
/// - **Single-Threaded**: Not thread-safe, cannot be sent across threads
/// - **Conditional Execution**: Only mutates when predicate returns `true`
/// - **No Lock Overhead**: More efficient than `ArcConditionalMutator`
///
/// # Examples
///
/// ```rust
/// use prism3_function::{Mutator, RcMutator};
///
/// let conditional = RcMutator::new(|x: &mut i32| *x *= 2)
///     .when(|x: &i32| *x > 0);
///
/// let conditional_clone = conditional.clone();
///
/// let mut value = 5;
/// let mut m = conditional;
/// m.mutate(&mut value);
/// assert_eq!(value, 10);
/// ```
///
/// # Author
///
/// Haixing Hu
pub struct RcConditionalMutator<T> {
    mutator: RcMutator<T>,
    predicate: RcPredicate<T>,
}
impl<T> Mutator<T> for RcConditionalMutator<T>
where
    T: 'static,
{
    fn mutate(&mut self, value: &mut T) {
        if self.predicate.test(value) {
            self.mutator.mutate(value);
        }
    }

    fn into_box(self) -> BoxMutator<T> {
        let pred = self.predicate;
        let mut mutator = self.mutator;
        BoxMutator::new(move |t| {
            if pred.test(t) {
                mutator.mutate(t);
            }
        })
    }

    fn into_rc(self) -> RcMutator<T> {
        let pred = self.predicate;
        let mut mutator = self.mutator;
        RcMutator::new(move |t| {
            if pred.test(t) {
                mutator.mutate(t);
            }
        })
    }

    // do NOT override Mutator::into_arc() because RcConditionalMutator is not Send + Sync
    // and calling RcConditionalMutator::into_arc() will cause a compile error

    fn into_fn(self) -> impl FnMut(&mut T) {
        let pred = self.predicate;
        let mut mutator = self.mutator;
        move |t: &mut T| {
            if pred.test(t) {
                mutator.mutate(t);
            }
        }
    }

    fn to_box(&self) -> BoxMutator<T>
    where
        Self: Sized + 'static,
        T: 'static,
    {
        self.clone().into_box()
    }

    fn to_rc(&self) -> RcMutator<T>
    where
        Self: Sized + 'static,
        T: 'static,
    {
        self.clone().into_rc()
    }

    // do NOT override Mutator::to_arc() because RcMutator is not Send + Sync
    // and calling RcMutator::to_arc() will cause a compile error

    fn to_fn(&self) -> impl FnMut(&mut T)
    where
        Self: Sized + 'static,
        T: 'static,
    {
        self.clone().into_fn()
    }
}

impl<T> RcConditionalMutator<T>
where
    T: 'static,
{
    /// Adds an else branch (single-threaded shared version)
    ///
    /// Executes the original mutator when the condition is satisfied, otherwise
    /// executes else_mutator.
    ///
    /// # Parameters
    ///
    /// * `else_mutator` - The mutator for the else branch. **Note: This parameter
    ///   is passed by value and will transfer ownership.** If you need to preserve
    ///   the original mutator, clone it first (if it implements `Clone`). Can be:
    ///   - A closure: `|x: &mut T|`
    ///   - An `RcMutator<T>`
    ///   - A `BoxMutator<T>`
    ///   - Any type implementing `Mutator<T>`
    ///
    /// # Returns
    ///
    /// Returns the composed `RcMutator<T>`
    ///
    /// # Examples
    ///
    /// ## Using a closure (recommended)
    ///
    /// ```rust
    /// use prism3_function::{Mutator, RcMutator};
    ///
    /// let mut mutator = RcMutator::new(|x: &mut i32| *x *= 2)
    ///     .when(|x: &i32| *x > 0)
    ///     .or_else(|x: &mut i32| *x -= 1);
    ///
    /// let mut positive = 5;
    /// mutator.mutate(&mut positive);
    /// assert_eq!(positive, 10);
    ///
    /// let mut negative = -5;
    /// mutator.mutate(&mut negative);
    /// assert_eq!(negative, -6);
    /// ```
    pub fn or_else<C>(self, else_mutator: C) -> RcMutator<T>
    where
        C: Mutator<T> + 'static,
    {
        let pred = self.predicate;
        let mut then_mut = self.mutator;
        let mut else_mut = else_mutator;

        RcMutator::new(move |t: &mut T| {
            if pred.test(t) {
                then_mut.mutate(t);
            } else {
                else_mut.mutate(t);
            }
        })
    }
}

impl<T> Clone for RcConditionalMutator<T> {
    /// Clones the conditional mutator
    ///
    /// Creates a new instance that shares the underlying mutator and predicate
    /// with the original instance.
    fn clone(&self) -> Self {
        RcConditionalMutator {
            mutator: self.mutator.clone(),
            predicate: self.predicate.clone(),
        }
    }
}

// ============================================================================
// 6. ArcMutator - Thread-Safe Shared Ownership Implementation
// ============================================================================

/// ArcMutator struct
///
/// A mutator implementation based on `Arc<Mutex<dyn FnMut(&mut T) + Send>>`
/// for thread-safe shared ownership scenarios. This type allows the mutator
/// to be safely shared and used across multiple threads.
///
/// # Features
///
/// - **Shared Ownership**: Cloneable via `Arc`, multiple owners allowed
/// - **Thread-Safe**: Implements `Send + Sync`, safe for concurrent use
/// - **Interior Mutability**: Uses `Mutex` for safe concurrent mutations
/// - **Mutable State**: Can modify captured environment via `FnMut`
/// - **Chainable**: Method chaining via `&self` (non-consuming)
///
/// # Use Cases
///
/// Choose `ArcMutator` when:
/// - The mutator needs to be shared across multiple threads
/// - Concurrent task processing (e.g., thread pools)
/// - Thread safety is required (Send + Sync)
///
/// # Examples
///
/// ```rust
/// use prism3_function::{Mutator, ArcMutator};
///
/// let mutator = ArcMutator::new(|x: &mut i32| *x *= 2);
/// let clone = mutator.clone();
///
/// let mut value = 5;
/// let mut m = mutator;
/// m.mutate(&mut value);
/// assert_eq!(value, 10);
/// ```
///
/// # Author
///
/// Haixing Hu
pub struct ArcMutator<T> {
    function: ArcMutMutatorFn<T>,
}

impl<T> ArcMutator<T>
where
    T: Send + 'static,
{
    /// Creates a new ArcMutator
    ///
    /// # Parameters
    ///
    /// * `f` - The closure to wrap
    ///
    /// # Returns
    ///
    /// Returns a new `ArcMutator<T>` instance
    ///
    /// # Examples
    ///
    /// ```rust
    /// use prism3_function::{Mutator, ArcMutator};
    ///
    /// let mutator = ArcMutator::new(|x: &mut i32| *x += 1);
    /// let mut value = 5;
    /// let mut m = mutator;
    /// m.mutate(&mut value);
    /// assert_eq!(value, 6);
    /// ```
    pub fn new<F>(f: F) -> Self
    where
        F: FnMut(&mut T) + Send + 'static,
    {
        ArcMutator {
            function: Arc::new(Mutex::new(f)),
        }
    }

    /// Creates a no-op mutator
    ///
    /// Returns a mutator that performs no operation.
    ///
    /// # Returns
    ///
    /// Returns a no-op mutator
    ///
    /// # Examples
    ///
    /// ```rust
    /// use prism3_function::{Mutator, ArcMutator};
    ///
    /// let noop = ArcMutator::<i32>::noop();
    /// let mut value = 42;
    /// let mut m = noop;
    /// m.mutate(&mut value);
    /// assert_eq!(value, 42); // Value unchanged
    /// ```
    pub fn noop() -> Self {
        ArcMutator::new(|_| {})
    }

    /// Chains another ArcMutator in sequence
    ///
    /// Returns a new mutator that first executes the current operation, then
    /// executes the next operation. Borrows &self, does not consume the
    /// original mutator.
    ///
    /// # Parameters
    ///
    /// * `next` - The mutator to execute after the current operation
    ///
    /// # Returns
    ///
    /// Returns a new composed `ArcMutator<T>`
    ///
    /// # Examples
    ///
    /// ```rust
    /// use prism3_function::{Mutator, ArcMutator};
    ///
    /// let first = ArcMutator::new(|x: &mut i32| *x *= 2);
    /// let second = ArcMutator::new(|x: &mut i32| *x += 10);
    ///
    /// let chained = first.and_then(&second);
    ///
    /// // first and second are still usable
    /// let mut value = 5;
    /// let mut m = chained;
    /// m.mutate(&mut value);
    /// assert_eq!(value, 20); // (5 * 2) + 10
    /// ```
    pub fn and_then(&self, next: &ArcMutator<T>) -> ArcMutator<T> {
        let first = Arc::clone(&self.function);
        let second = Arc::clone(&next.function);
        ArcMutator {
            function: Arc::new(Mutex::new(move |t: &mut T| {
                (first.lock().unwrap())(t);
                (second.lock().unwrap())(t);
            })),
        }
    }

    /// Creates a conditional mutator (thread-safe version)
    ///
    /// Returns a mutator that only executes when a predicate is satisfied.
    ///
    /// # Parameters
    ///
    /// * `predicate` - The condition to check. **Note: This parameter is passed
    ///   by value and will transfer ownership.** If you need to preserve the
    ///   original predicate, clone it first (if it implements `Clone`).
    ///   Must be `Send + Sync`, can be:
    ///   - A closure: `|x: &T| -> bool` (requires `Send + Sync`)
    ///   - A function pointer: `fn(&T) -> bool`
    ///   - An `ArcPredicate<T>`
    ///   - Any type implementing `Predicate<T> + Send + Sync`
    ///
    /// # Returns
    ///
    /// Returns `ArcConditionalMutator<T>`
    ///
    /// # Examples
    ///
    /// ```rust
    /// use prism3_function::{Mutator, ArcMutator};
    ///
    /// let mutator = ArcMutator::new(|x: &mut i32| *x *= 2);
    /// let conditional = mutator.when(|x: &i32| *x > 0);
    ///
    /// let conditional_clone = conditional.clone();
    ///
    /// let mut positive = 5;
    /// let mut m = conditional;
    /// m.mutate(&mut positive);
    /// assert_eq!(positive, 10);
    /// ```
    pub fn when<P>(&self, predicate: P) -> ArcConditionalMutator<T>
    where
        P: Predicate<T> + Send + Sync + 'static,
        T: Send + Sync,
    {
        ArcConditionalMutator {
            mutator: self.clone(),
            predicate: predicate.into_arc(),
        }
    }
}

impl<T> Mutator<T> for ArcMutator<T> {
    fn mutate(&mut self, value: &mut T) {
        (self.function.lock().unwrap())(value)
    }

    fn into_box(self) -> BoxMutator<T>
    where
        T: 'static,
    {
        BoxMutator::new(move |t| self.function.lock().unwrap()(t))
    }

    fn into_rc(self) -> RcMutator<T>
    where
        T: 'static,
    {
        RcMutator::new(move |t| self.function.lock().unwrap()(t))
    }

    fn into_arc(self) -> ArcMutator<T>
    where
        T: Send + 'static,
    {
        self
    }

    fn into_fn(self) -> impl FnMut(&mut T)
    where
        Self: Sized + 'static,
        T: 'static,
    {
        move |t| self.function.lock().unwrap()(t)
    }

    fn to_box(&self) -> BoxMutator<T>
    where
        Self: Sized + 'static,
        T: 'static,
    {
        let self_fn = self.function.clone();
        BoxMutator::new(move |t| self_fn.lock().unwrap()(t))
    }

    fn to_rc(&self) -> RcMutator<T>
    where
        Self: Sized + 'static,
        T: 'static,
    {
        let self_fn = self.function.clone();
        RcMutator::new(move |t| self_fn.lock().unwrap()(t))
    }

    fn to_arc(&self) -> ArcMutator<T>
    where
        Self: Sized + Send + 'static,
        T: Send + 'static,
    {
        self.clone()
    }

    fn to_fn(&self) -> impl FnMut(&mut T)
    where
        Self: Sized + 'static,
        T: 'static,
    {
        let self_fn = self.function.clone();
        move |t| self_fn.lock().unwrap()(t)
    }
}

impl<T> Clone for ArcMutator<T> {
    /// Clones the ArcMutator
    ///
    /// Creates a new ArcMutator that shares the underlying function with the
    /// original instance.
    fn clone(&self) -> Self {
        ArcMutator {
            function: self.function.clone(),
        }
    }
}

// ============================================================================
// 7. ArcConditionalMutator - Arc-based Conditional Mutator
// ============================================================================

/// ArcConditionalMutator struct
///
/// A thread-safe conditional mutator that only executes when a predicate is
/// satisfied. Uses `ArcMutator` and `ArcPredicate` for shared ownership across
/// threads.
///
/// This type is typically created by calling `ArcMutator::when()` and is
/// designed to work with the `or_else()` method to create if-then-else logic.
///
/// # Features
///
/// - **Shared Ownership**: Cloneable via `Arc`, multiple owners allowed
/// - **Thread-Safe**: Implements `Send + Sync`, safe for concurrent use
/// - **Conditional Execution**: Only mutates when predicate returns `true`
/// - **Chainable**: Can add `or_else` branch to create if-then-else logic
///
/// # Examples
///
/// ```rust
/// use prism3_function::{Mutator, ArcMutator};
///
/// let conditional = ArcMutator::new(|x: &mut i32| *x *= 2)
///     .when(|x: &i32| *x > 0);
///
/// let conditional_clone = conditional.clone();
///
/// let mut value = 5;
/// let mut m = conditional;
/// m.mutate(&mut value);
/// assert_eq!(value, 10);
/// ```
///
/// # Author
///
/// Haixing Hu
pub struct ArcConditionalMutator<T> {
    mutator: ArcMutator<T>,
    predicate: ArcPredicate<T>,
}
impl<T> Mutator<T> for ArcConditionalMutator<T>
where
    T: Send + 'static,
{
    fn mutate(&mut self, value: &mut T) {
        if self.predicate.test(value) {
            self.mutator.mutate(value);
        }
    }

    fn into_box(self) -> BoxMutator<T>
    where
        T: 'static,
    {
        let pred = self.predicate;
        let mut mutator = self.mutator;
        BoxMutator::new(move |t| {
            if pred.test(t) {
                mutator.mutate(t);
            }
        })
    }

    fn into_rc(self) -> RcMutator<T>
    where
        T: 'static,
    {
        let pred = self.predicate.to_rc();
        let mutator = self.mutator.into_rc();
        let mut mutator_fn = mutator;
        RcMutator::new(move |t| {
            if pred.test(t) {
                mutator_fn.mutate(t);
            }
        })
    }

    fn into_arc(self) -> ArcMutator<T>
    where
        T: Send + 'static,
    {
        let pred = self.predicate;
        let mut mutator = self.mutator;
        ArcMutator::new(move |t| {
            if pred.test(t) {
                mutator.mutate(t);
            }
        })
    }

    fn into_fn(self) -> impl FnMut(&mut T)
    where
        T: 'static,
    {
        let pred = self.predicate;
        let mut mutator = self.mutator;
        move |t: &mut T| {
            if pred.test(t) {
                mutator.mutate(t);
            }
        }
    }

    fn to_box(&self) -> BoxMutator<T>
    where
        Self: Sized + 'static,
        T: 'static,
    {
        self.clone().into_box()
    }

    fn to_rc(&self) -> RcMutator<T>
    where
        Self: Sized + 'static,
        T: 'static,
    {
        self.clone().into_rc()
    }

    fn to_arc(&self) -> ArcMutator<T>
    where
        Self: Sized + 'static,
        T: 'static,
    {
        self.clone().into_arc()
    }

    fn to_fn(&self) -> impl FnMut(&mut T)
    where
        Self: Sized + 'static,
        T: 'static,
    {
        self.clone().into_fn()
    }
}

impl<T> ArcConditionalMutator<T>
where
    T: Send + 'static,
{
    /// Adds an else branch (thread-safe version)
    ///
    /// Executes the original mutator when the condition is satisfied, otherwise
    /// executes else_mutator.
    ///
    /// # Parameters
    ///
    /// * `else_mutator` - The mutator for the else branch. **Note: This parameter
    ///   is passed by value and will transfer ownership.** If you need to preserve
    ///   the original mutator, clone it first (if it implements `Clone`).
    ///   Must be `Send`, can be:
    ///   - A closure: `|x: &mut T|` (must be `Send`)
    ///   - An `ArcMutator<T>`
    ///   - A `BoxMutator<T>`
    ///   - Any type implementing `Mutator<T> + Send`
    ///
    /// # Returns
    ///
    /// Returns the composed `ArcMutator<T>`
    ///
    /// # Examples
    ///
    /// ## Using a closure (recommended)
    ///
    /// ```rust
    /// use prism3_function::{Mutator, ArcMutator};
    ///
    /// let mut mutator = ArcMutator::new(|x: &mut i32| *x *= 2)
    ///     .when(|x: &i32| *x > 0)
    ///     .or_else(|x: &mut i32| *x -= 1);
    ///
    /// let mut positive = 5;
    /// mutator.mutate(&mut positive);
    /// assert_eq!(positive, 10);
    ///
    /// let mut negative = -5;
    /// mutator.mutate(&mut negative);
    /// assert_eq!(negative, -6);
    /// ```
    pub fn or_else<C>(&self, else_mutator: C) -> ArcMutator<T>
    where
        C: Mutator<T> + Send + 'static,
        T: Send + Sync,
    {
        let pred = self.predicate.clone();
        let mut then_mut = self.mutator.clone();
        let mut else_mut = else_mutator;
        ArcMutator::new(move |t: &mut T| {
            if pred.test(t) {
                then_mut.mutate(t);
            } else {
                else_mut.mutate(t);
            }
        })
    }
}

impl<T> Clone for ArcConditionalMutator<T> {
    /// Clones the conditional mutator
    ///
    /// Creates a new instance that shares the underlying mutator and predicate
    /// with the original instance.
    fn clone(&self) -> Self {
        ArcConditionalMutator {
            mutator: self.mutator.clone(),
            predicate: self.predicate.clone(),
        }
    }
}

// ============================================================================
// 8. Implement Mutator trait for closures
// ============================================================================

impl<T, F> Mutator<T> for F
where
    F: FnMut(&mut T),
{
    fn mutate(&mut self, value: &mut T) {
        self(value)
    }

    fn into_box(self) -> BoxMutator<T>
    where
        Self: Sized + 'static,
        T: 'static,
    {
        BoxMutator::new(self)
    }

    fn into_rc(self) -> RcMutator<T>
    where
        Self: Sized + 'static,
        T: 'static,
    {
        RcMutator::new(self)
    }

    fn into_arc(self) -> ArcMutator<T>
    where
        Self: Sized + Send + 'static,
        T: Send + 'static,
    {
        ArcMutator::new(self)
    }

    fn into_fn(self) -> impl FnMut(&mut T)
    where
        Self: Sized + 'static,
        T: 'static,
    {
        self
    }

    fn to_box(&self) -> BoxMutator<T>
    where
        Self: Sized + Clone + 'static,
        T: 'static,
    {
        let cloned = self.clone();
        BoxMutator::new(cloned)
    }

    fn to_rc(&self) -> RcMutator<T>
    where
        Self: Sized + Clone + 'static,
        T: 'static,
    {
        let cloned = self.clone();
        RcMutator::new(cloned)
    }

    fn to_arc(&self) -> ArcMutator<T>
    where
        Self: Sized + Clone + Send + 'static,
        T: Send + 'static,
    {
        let cloned = self.clone();
        ArcMutator::new(cloned)
    }

    fn to_fn(&self) -> impl FnMut(&mut T)
    where
        Self: Sized + Clone + 'static,
        T: 'static,
    {
        self.clone()
    }
}

// ============================================================================
// 9. Provide extension methods for closures
// ============================================================================

// ============================================================================
// 7. Provide extension methods for closures
// ============================================================================

/// Extension trait providing mutator composition methods for closures
///
/// Provides `and_then` and other composition methods for all closures that
/// implement `FnMut(&mut T)`, enabling direct method chaining on closures
/// without explicit wrapper types.
///
/// # Features
///
/// - **Natural Syntax**: Chain operations directly on closures
/// - **Returns BoxMutator**: Composition results are `BoxMutator<T>` for
///   continued chaining
/// - **Zero Cost**: No overhead when composing closures
/// - **Automatic Implementation**: All `FnMut(&mut T)` closures get these
///   methods automatically
///
/// # Examples
///
/// ```rust
/// use prism3_function::{Mutator, FnMutatorOps};
///
/// let chained = (|x: &mut i32| *x *= 2)
///     .and_then(|x: &mut i32| *x += 10);
/// let mut value = 5;
/// let mut result = chained;
/// result.mutate(&mut value);
/// assert_eq!(value, 20); // (5 * 2) + 10
/// ```
///
/// # Author
///
/// Haixing Hu
pub trait FnMutatorOps<T>: FnMut(&mut T) + Sized {
    /// Chains another mutator in sequence
    ///
    /// Returns a new mutator that first executes the current operation, then
    /// executes the next operation. Consumes the current closure and returns
    /// `BoxMutator<T>`.
    ///
    /// # Parameters
    ///
    /// * `next` - The mutator to execute after the current operation. **Note:
    ///   This parameter is passed by value and will transfer ownership.** If you
    ///   need to preserve the original mutator, clone it first (if it implements
    ///   `Clone`). Can be:
    ///   - A closure: `|x: &mut T|`
    ///   - A `BoxMutator<T>`
    ///   - An `ArcMutator<T>`
    ///   - An `RcMutator<T>`
    ///   - Any type implementing `Mutator<T>`
    ///
    /// # Returns
    ///
    /// Returns the composed `BoxMutator<T>`
    ///
    /// # Examples
    ///
    /// ```rust
    /// use prism3_function::{Mutator, FnMutatorOps};
    ///
    /// let chained = (|x: &mut i32| *x *= 2)
    ///     .and_then(|x: &mut i32| *x += 10)
    ///     .and_then(|x: &mut i32| println!("Result: {}", x));
    ///
    /// let mut value = 5;
    /// let mut result = chained;
    /// result.mutate(&mut value); // Prints: Result: 20
    /// assert_eq!(value, 20);
    /// ```
    fn and_then<C>(self, next: C) -> BoxMutator<T>
    where
        Self: 'static,
        C: Mutator<T> + 'static,
        T: 'static,
    {
        let mut first = self;
        let mut second = next.into_fn();
        BoxMutator::new(move |t| {
            (first)(t);
            second(t);
        })
    }
}

/// Implements FnMutatorOps for all closure types
impl<T, F> FnMutatorOps<T> for F where F: FnMut(&mut T) {}