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 `BoxFunctionOnce` public type.

use crate::BoxConditionalFunctionOnce;
use crate::FunctionOnce;
use crate::Predicate;
use crate::functions::macros::impl_box_function_methods;
use crate::functions::macros::impl_function_common_methods;
use crate::functions::macros::impl_function_constant_method;
use crate::functions::macros::impl_function_debug_display;
use crate::functions::macros::impl_function_identity_method;
use crate::macros::impl_closure_once_trait;

// ============================================================================
// BoxFunctionOnce - Box<dyn FnOnce(&T) -> R>
// ============================================================================

/// BoxFunctionOnce - consuming transformer wrapper based on
/// `Box<dyn FnOnce>`
///
/// A transformer wrapper that provides single ownership with one-time use
/// semantics. Calling it consumes the wrapper and borrows the input value.
///
/// # Type Parameters
///
/// - `T`: The input type borrowed by the callback.
/// - `R`: The output type returned by the callback.
///
/// # Features
///
/// - **Based on**: `Box<dyn FnOnce(&T) -> R>`
/// - **Ownership**: Single ownership, cannot be cloned
/// - **Reusability**: Can only be called once (consumes self)
/// - **Thread Safety**: Not thread-safe (no `Send + Sync` requirement)
///
/// # Examples
///
/// ```
/// use qubit_function::{BoxFunctionOnce, FunctionOnce};
///
/// let double = BoxFunctionOnce::new(|value: &i32| value * 2);
/// assert_eq!(double.apply(&21), 42);
/// ```
#[must_use = "callback wrappers do nothing unless stored or invoked"]
pub struct BoxFunctionOnce<T, R> {
    /// The wrapped callback implementation.
    pub(super) function: Box<dyn FnOnce(&T) -> R>,
    /// Diagnostic metadata associated with this callback.
    pub(super) metadata: crate::internal::CallbackMetadata,
}

impl<T, R> BoxFunctionOnce<T, R> {
    // Generates: new(), new_with_name(), new_with_optional_name(), name(),
    // set_name()
    impl_function_common_methods!(
        BoxFunctionOnce<T, R>,
        (FnOnce(&T) -> R + 'static),
        |f| Box::new(f)
    );

    // Generates: when(), and_then(), compose()
    impl_box_function_methods!(
        BoxFunctionOnce<T, R>,
        BoxConditionalFunctionOnce,
        FunctionOnce
    );
}

impl<T, R> FunctionOnce<T, R> for BoxFunctionOnce<T, R> {
    #[inline(always)]
    fn apply(self, input: &T) -> R {
        (self.function)(input)
    }
}

// Generates: constant() method for BoxFunctionOnce<T, R>
impl_function_constant_method!(BoxFunctionOnce<T, R>, 'static);

// Generates: identity() method for BoxFunctionOnce<T, T>
impl_function_identity_method!(BoxFunctionOnce<T, T>, FunctionOnce);

// Generates: Debug and Display implementations for BoxFunctionOnce<T, R>
impl_function_debug_display!(BoxFunctionOnce<T, R>);

// ============================================================================
// Blanket implementation for standard FnOnce trait
// ============================================================================

// Implement FunctionOnce for all FnOnce(&T) -> R using macro
impl_closure_once_trait!(
    FunctionOnce<T, R>,
    apply,
    BoxFunctionOnce,
    FnOnce(input: &T) -> R
);