qubit-function 0.18.2

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 `RcConditionalConsumer` public type.

use crate::Consumer;
use crate::Predicate;
use crate::RcConsumer;
use crate::RcPredicate;
use crate::consumers::macros::impl_conditional_consumer_clone;
use crate::consumers::macros::impl_conditional_consumer_debug_display;
use crate::consumers::macros::impl_shared_conditional_consumer;

// ============================================================================
// 8. RcConditionalConsumer - Rc-based Conditional Consumer
// ============================================================================

/// A single-threaded shared consumer that runs only when its predicate accepts
/// the input.
///
/// It shares its callback and predicate through `Rc`, and can be created with
/// [`RcConsumer::when`]. Use [`or_else`](Self::or_else) to add a callback for
/// inputs rejected by the predicate. Since it uses `Rc`, this type is not
/// thread-safe and cannot be sent between threads.
///
/// This type is typically created by calling `RcConsumer::when()` and is
/// designed to work with the `or_else()` method to create if-then-else logic.
///
/// # Features
///
/// - **Shared Ownership**: Cloneable through `Rc`, allows multiple owners
/// - **Single-threaded**: Not thread-safe, cannot be sent across threads
/// - **Conditional Execution**: Only consumes when predicate returns `true`
/// - **Chainable**: Can add `or_else` branch to create if-then-else logic
/// - **Implements Consumer**: Can be used anywhere a `Consumer` is expected
/// - **Shared access**: Receives `&self` and `&T`; interior mutability and
///   external side effects remain possible
///
/// # Type Parameters
///
/// * `T` - The input type borrowed by the predicate and consumer callbacks.
///
/// # Examples
///
/// ## Basic Conditional Execution
///
/// ```rust
/// use qubit_function::{Consumer, RcConsumer};
///
/// let consumer = RcConsumer::new(|x: &i32| {
///     println!("Positive: {}", x);
/// });
/// let conditional = consumer.when(|x: &i32| *x > 0);
///
/// conditional.accept(&5);  // Prints: Positive: 5
/// conditional.accept(&-5); // Does nothing
/// ```
///
/// ## With or_else Branch
///
/// ```rust
/// use qubit_function::{Consumer, RcConsumer};
///
/// let consumer = RcConsumer::new(|x: &i32| {
///     println!("Positive: {}", x);
/// })
/// .when(|x: &i32| *x > 0)
/// .or_else(|x: &i32| {
///     println!("Non-positive: {}", x);
/// });
///
/// consumer.accept(&5);  // Prints: Positive: 5
/// consumer.accept(&-5); // Prints: Non-positive: -5
/// ```
#[must_use = "callback wrappers do nothing unless stored or invoked"]
pub struct RcConditionalConsumer<T> {
    /// The wrapped consumer callback.
    pub(super) consumer: RcConsumer<T>,
    /// The predicate controlling conditional execution.
    pub(super) predicate: RcPredicate<T>,
}

// Use macro to generate conditional consumer implementations
impl_shared_conditional_consumer!(
    RcConditionalConsumer<T>,
    RcConsumer,
    Consumer,
    callback_bounds = ('static)
);

// Hand-written Consumer trait implementation
impl<T> Consumer<T> for RcConditionalConsumer<T> {
    fn accept(&self, value: &T) {
        if self.predicate.test(value) {
            self.consumer.accept(value);
        }
    }
}

// Use macro to generate Clone implementation
impl_conditional_consumer_clone!(RcConditionalConsumer<T>);

// Use macro to generate Debug and Display implementations
impl_conditional_consumer_debug_display!(RcConditionalConsumer<T>);