qubit-function 0.16.0

Functional programming traits and Box/Rc/Arc adapters for Rust, inspired by Java functional interfaces
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// =============================================================================
//    Copyright (c) 2025 - 2026 Haixing Hu.
//
//    SPDX-License-Identifier: Apache-2.0
//
//    Licensed under the Apache License, Version 2.0.
// =============================================================================
//! Defines the `RcConditionalFunction` public type.

use {
    crate::Function,
    crate::Predicate,
    crate::RcFunction,
    crate::RcPredicate,
    crate::functions::macros::impl_conditional_function_clone,
    crate::functions::macros::impl_conditional_function_debug_display,
    crate::functions::macros::impl_shared_conditional_function,
};

// ============================================================================
// RcConditionalFunction - Rc-based Conditional Function
// ============================================================================

/// RcConditionalFunction struct
///
/// A single-threaded conditional function that only executes when a
/// predicate is satisfied. Uses `RcFunction` and `RcPredicate` for shared
/// ownership within a single thread.
///
/// This type is typically created by calling `RcFunction::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 transforms when predicate returns `true`
/// - **Ownership Cost**: `Rc` uses non-atomic reference counting; `Arc` uses
///   atomic reference counting, and neither wrapper locks callback invocation
///
/// # Examples
///
/// ```rust
/// use qubit_function::{Function, RcFunction};
///
/// let double = RcFunction::new(|x: &i32| x * 2);
/// let identity = RcFunction::<i32, i32>::identity();
/// let conditional = double.when(|x: &i32| *x > 0).or_else(identity);
///
/// let conditional_clone = conditional.clone();
///
/// assert_eq!(conditional.apply(&5), 10);
/// assert_eq!(conditional_clone.apply(&-5), -5);
/// ```
#[must_use = "callback wrappers do nothing unless stored or invoked"]
pub struct RcConditionalFunction<T, R> {
    /// The wrapped callback implementation.
    pub(super) function: RcFunction<T, R>,
    /// The predicate controlling conditional execution.
    pub(super) predicate: RcPredicate<T>,
}

// Use macro to generate conditional function implementations
impl_shared_conditional_function!(
    RcConditionalFunction<T, R>,
    RcFunction,
    Function,
    callback_bounds = ('static)
);

// Use macro to generate conditional function clone implementations
impl_conditional_function_clone!(RcConditionalFunction<T, R>);

// Use macro to generate conditional function debug and display implementations
impl_conditional_function_debug_display!(RcConditionalFunction<T, R>);