qubit-function 0.16.0

// =============================================================================
//    Copyright (c) 2025 - 2026 Haixing Hu.
//
//    SPDX-License-Identifier: Apache-2.0
//
//    Licensed under the Apache License, Version 2.0.
// =============================================================================
//! Defines the `BoxStatefulBiConsumer` public type.

use {
    crate::BiPredicate,
    crate::BoxConditionalStatefulBiConsumer,
};
use {
    crate::StatefulBiConsumer,
    crate::consumers::macros::impl_box_consumer_methods,
    crate::consumers::macros::impl_consumer_common_methods,
    crate::consumers::macros::impl_consumer_debug_display,
};

/// The erased callback representation used by this implementation.
type BoxStatefulBiConsumerFn<T, U> = Box<dyn FnMut(&T, &U)>;

// =======================================================================
// 2. BoxStatefulBiConsumer - Single Ownership Implementation
// =======================================================================

/// BoxStatefulBiConsumer struct
///
/// A bi-consumer implementation based on `Box<dyn FnMut(&T, &U)>` for
/// single ownership scenarios. This is the simplest and most efficient
/// bi-consumer type when sharing is not required.
///
/// # Features
///
/// - **Single Ownership**: Not cloneable, ownership moves on use
/// - **Runtime cost**: One heap allocation and dynamic dispatch; no reference
///   counting or locking
/// - **Mutable State**: Can modify captured environment via `FnMut`
/// - **Builder Pattern**: Method chaining consumes `self` naturally
///
/// # Use Cases
///
/// Choose `BoxStatefulBiConsumer` when:
/// - The bi-consumer is used only once or in a linear flow
/// - Building pipelines where ownership naturally flows
/// - No need to share the consumer across contexts
/// - Performance is critical and sharing overhead is unacceptable
///
/// # Performance
///
/// `BoxStatefulBiConsumer` has the best performance among the three bi-consumer
/// 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 qubit_function::{BiConsumer, BoxStatefulBiConsumer, StatefulBiConsumer};
/// use std::sync::{Arc, Mutex};
///
/// let log = Arc::new(Mutex::new(Vec::new()));
/// let l = log.clone();
/// let mut consumer = BoxStatefulBiConsumer::new(move |x: &i32, y: &i32| {
///     l.lock().expect("mutex should not be poisoned").push(*x + *y);
/// });
/// consumer.accept(&5, &3);
/// assert_eq!(*log.lock().expect("mutex should not be poisoned"), vec![8]);
/// ```
#[must_use = "callback wrappers do nothing unless stored or invoked"]
pub struct BoxStatefulBiConsumer<T, U> {
    /// The wrapped callback implementation.
    pub(super) function: BoxStatefulBiConsumerFn<T, U>,
    /// Diagnostic metadata associated with this callback.
    pub(super) metadata: crate::internal::CallbackMetadata,
}

impl<T, U> BoxStatefulBiConsumer<T, U> {
    // Generates: new(), new_with_name(), name(), set_name(), noop()
    impl_consumer_common_methods!(
        BoxStatefulBiConsumer<T, U>,
        (FnMut(&T, &U) + 'static),
        |f| Box::new(f)
    );

    // Generates: when() and and_then() methods that consume self
    impl_box_consumer_methods!(
        BoxStatefulBiConsumer<T, U>,
        BoxConditionalStatefulBiConsumer,
        StatefulBiConsumer
    );
}

impl<T, U> StatefulBiConsumer<T, U> for BoxStatefulBiConsumer<T, U> {
    #[inline(always)]
    fn accept(&mut self, first: &T, second: &U) {
        (self.function)(first, second)
    }
}

// Use macro to generate Debug and Display implementations
impl_consumer_debug_display!(BoxStatefulBiConsumer<T, U>);