yoke/
zero_from.rs

1// This file is part of ICU4X. For terms of use, please see the file
2// called LICENSE at the top level of the ICU4X source tree
3// (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).
4
5use crate::trait_hack::YokeTraitHack;
6use crate::Yoke;
7use crate::Yokeable;
8
9use core::ops::Deref;
10use stable_deref_trait::StableDeref;
11
12use crate::ZeroFrom;
13
14impl<'zf, C: ?Sized, T> ZeroFrom<'zf, C> for YokeTraitHack<T>
15where
16    T: ZeroFrom<'zf, C>,
17{
18    #[inline]
19    fn zero_from(cart: &'zf C) -> Self {
20        YokeTraitHack(T::zero_from(cart))
21    }
22}
23
24impl<Y, C> Yoke<Y, C>
25where
26    Y: for<'a> Yokeable<'a>,
27    for<'a> YokeTraitHack<<Y as Yokeable<'a>>::Output>: ZeroFrom<'a, <C as Deref>::Target>,
28    C: StableDeref + Deref,
29    <C as Deref>::Target: 'static,
30{
31    /// Construct a [`Yoke`]`<Y, C>` from a cart implementing `StableDeref` by zero-copy cloning
32    /// the cart to `Y` and then yokeing that object to the cart.
33    ///
34    /// The type `Y` must implement [`ZeroFrom`]`<C::Target>`. This trait is auto-implemented
35    /// on many common types and can be custom implemented or derived in order to make it easier
36    /// to construct a `Yoke`.
37    ///
38    /// # Example
39    ///
40    /// Attach to a cart:
41    ///
42    /// ```
43    /// use std::borrow::Cow;
44    /// use yoke::Yoke;
45    ///
46    /// let yoke = Yoke::<Cow<'static, str>, String>::attach_to_zero_copy_cart(
47    ///     "demo".to_owned(),
48    /// );
49    ///
50    /// assert_eq!("demo", yoke.get());
51    /// ```
52    pub fn attach_to_zero_copy_cart(cart: C) -> Self {
53        Yoke::<Y, C>::attach_to_cart(cart, |c| {
54            YokeTraitHack::<<Y as Yokeable>::Output>::zero_from(c).0
55        })
56    }
57}