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 `BoxStatefulTransformer` public type.

use crate::BoxConditionalStatefulTransformer;
use crate::Predicate;
use crate::StatefulTransformer;
use crate::transformers::macros::impl_box_transformer_methods;
use crate::transformers::macros::impl_transformer_common_methods;
use crate::transformers::macros::impl_transformer_constant_method;
use crate::transformers::macros::impl_transformer_debug_display;

// ============================================================================
// BoxStatefulTransformer - Box<dyn FnMut(T) -> R>
// ============================================================================

/// BoxStatefulTransformer - transformer wrapper based on `Box<dyn FnMut>`
///
/// A transformer wrapper that provides single ownership with reusable stateful
/// transformation. The transformer consumes the input and can be called
/// multiple times while maintaining internal state.
///
/// # Features
///
/// - **Based on**: `Box<dyn FnMut(T) -> R>`
/// - **Ownership**: Single ownership, cannot be cloned
/// - **Reusability**: Can be called multiple times (each call consumes its
///   input)
/// - **Thread Safety**: Not thread-safe (no `Send + Sync` requirement)
/// - **Statefulness**: Can modify internal state between calls
///
/// # Type Parameters
///
/// * `T` - The input type consumed by the wrapped callback.
/// * `R` - The output type produced by the wrapped callback.
///
/// # Examples
///
/// ```
/// use qubit_function::{BoxStatefulTransformer, StatefulTransformer};
///
/// let mut transformer = BoxStatefulTransformer::new(|value: i32| value * 2);
/// assert_eq!(transformer.apply(3), 6);
/// ```
#[must_use = "callback wrappers do nothing unless stored or invoked"]
pub struct BoxStatefulTransformer<T, R> {
    /// The wrapped callback implementation.
    pub(super) function: Box<dyn FnMut(T) -> R>,
    /// Diagnostic metadata associated with this callback.
    pub(super) metadata: crate::internal::CallbackMetadata,
}

impl<T, R> BoxStatefulTransformer<T, R> {
    impl_transformer_common_methods!(
        BoxStatefulTransformer<T, R>,
        (FnMut(T) -> R + 'static),
        |f| Box::new(f)
    );

    impl_box_transformer_methods!(
        BoxStatefulTransformer<T, R>,
        BoxConditionalStatefulTransformer,
        StatefulTransformer
    );
}

// Implement constant method for BoxStatefulTransformer
impl_transformer_constant_method!(stateful BoxStatefulTransformer<T, R>);

// Implement Debug and Display for BoxStatefulTransformer
impl_transformer_debug_display!(BoxStatefulTransformer<T, R>);

// Implement StatefulTransformer trait for BoxStatefulTransformer
impl<T, R> StatefulTransformer<T, R> for BoxStatefulTransformer<T, R> {
    #[inline(always)]
    fn apply(&mut self, input: T) -> R {
        (self.function)(input)
    }
}