gear-common 2.0.0-pre.1

// Copyright (C) Gear Technologies Inc.
// SPDX-License-Identifier: GPL-3.0-or-later WITH Classpath-exception-2.0

//! Module for callback primitives.
//!
//! Callbacks represent some additional logic which
//! should be done over the argument on some conditions.

/// Represents callback action for cases `(&T) -> R`,
/// where `R` is `()` by default.
pub trait Callback<T, R = ()> {
    /// Triggers the callback's logic.
    fn call(arg: &T) -> R;
}

// Blank `Callback<T, ()>` implementation
// for skipping callback type in parent traits.
impl<T> Callback<T> for () {
    fn call(_: &T) {}
}

/// Represents callback action for cases
/// without input and output.
pub trait EmptyCallback {
    /// Triggers the callback's logic.
    fn call();
}

// Blank `EmptyCallback` implementation
// for skipping callback type in parent traits.
impl EmptyCallback for () {
    fn call() {}
}

/// Represents callback action for cases `(&T) -> Result<R, E>`,
/// where `R` is `()` by default and `E` is associated type `Error`.
pub trait FallibleCallback<T, R = ()> {
    /// Returning error in callback's `Err` case.
    type Error;

    /// Triggers the callback's logic.
    fn call(arg: &T) -> Result<R, Self::Error>;
}

/// Represents callback action for cases
/// without input for getting some data.
pub trait GetCallback<T> {
    /// Returns value by callback's logic.
    fn call() -> T;
}

// Blank `GetCallback` implementation
// for returning default values.
impl<T: Default> GetCallback<T> for () {
    fn call() -> T {
        Default::default()
    }
}

/// Represents transposing callback
/// for mutating values.
pub trait TransposeCallback<T, R> {
    /// Returns value by callback's logic.
    fn call(arg: T) -> R;
}

// Blank `TransposeCallback` implementation
// for returning value itself.
impl<T> TransposeCallback<T, T> for () {
    fn call(arg: T) -> T {
        arg
    }
}