CODEWITHSUNDEEP
rust
Simon Warta
Simon Warta

Reputation: 11408

Does the Rust stable standard library use unstable features?

In the Rust standard library, you can see implementations like this which use const generics:

#[stable(feature = "vec_from_array", since = "1.44.0")]
impl<T, const N: usize> From<[T; N]> for Vec<T> {
    #[cfg(not(test))]
    fn from(s: [T; N]) -> Vec<T> {
        <[T]>::into_vec(box s)
    }
    #[cfg(test)]
    fn from(s: [T; N]) -> Vec<T> {
        crate::slice::into_vec(box s)
    }
}

When I try to do the same in my code

impl<const N: usize> From<[u8; N]> for Binary {
    fn from(source: [u8; N]) -> Self {
        // Implementation available for $N <= 32.
        // Requires https://caniuse.rs/features/vec_from_array, avaiable since Rust 1.44.0.
        Self(source.into())
    }
}

I get the error

   --> packages/std/src/binary.rs:105:12
    |
105 | impl<const N: usize> From<[u8; N]> for Binary {
    |            ^
    |
    = note: see issue #74878 <https://github.com/rust-lang/rust/issues/74878> for more information

I'm using Rust 1.47.0.

Does this mean the Rust stable standard library is compiled with unstable features?

Upvotes: 3

Views: 1560

Answers (1)

Shepmaster
Shepmaster

Reputation: 430673

Yes, it uses unstable features. — Peter Hall

For Rust 1.47.0's liballoc (where Vec is defined), it uses sixty or so unstable features.

See also:

Upvotes: 9

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