gecko-dev/servo/components/style/sink.rs

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

//! Small helpers to abstract over different containers.
#![deny(missing_docs)]

use smallvec::{Array, SmallVec};
use std::marker::PhantomData;

/// A trait to abstract over a `push` method that may be implemented for
/// different kind of types.
///
/// Used to abstract over `Array`, `SmallVec` and `Vec`, and also to implement a
/// type which `push` method does only tweak a byte when we only need to check
/// for the presence of something.
pub trait Push<T> {
    /// Push a value into self.
    fn push(&mut self, value: T);
}

impl<T> Push<T> for Vec<T> {
    fn push(&mut self, value: T) {
        Vec::push(self, value);
    }
}

impl<A: Array> Push<A::Item> for SmallVec<A> {
    fn push(&mut self, value: A::Item) {
        SmallVec::push(self, value);
    }
}

/// A struct that implements `Push`, but only stores whether it's empty.
pub struct ForgetfulSink<T>(bool, PhantomData<T>);

impl<T> ForgetfulSink<T> {
    /// Trivially construct a new `ForgetfulSink`.
    pub fn new() -> Self {
        ForgetfulSink(true, PhantomData)
    }

    /// Whether this sink is empty or not.
    pub fn is_empty(&self) -> bool {
        self.0
    }
}

impl<T> Push<T> for ForgetfulSink<T> {
    fn push(&mut self, _value: T) {
        self.0 = false;
    }
}