// This file is part of ICU4X. For terms of use, please see the file

// called LICENSE at the top level of the ICU4X source tree

// (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).

use crate::Yokeable;

/// This method casts `yokeable` between `&'a mut Y<'static>` and `&'a mut Y<'a>`,

/// and passes it to `f`.

///

/// See [`Yokeable::transform_mut`] for why this is safe, noting that no `'static` return type

/// can leak data from the cart or Yokeable.

#[inline]

pub(crate) fn transform_mut_yokeable<'a, Y, F, R>(yokeable: &'a mut Y, f: F) -> R

where

    Y: Yokeable<'a>,

    // be VERY CAREFUL changing this signature, it is very nuanced

    F: 'static + for<'b> FnOnce(&'b mut Y::Output) -> R,

    R: 'static,

{

    // Cast away the lifetime of `Y`

    // Safety: this is equivalent to f(transmute(yokeable)), and the documentation of

    // [`Yokeable::transform_mut`] and this function explain why doing so is sound.

    let y = unsafe { &mut *(yokeable as *mut Y as *mut Y::Output).cast() };

    f(y)

}