Concat in std::slice - Rust (original) (raw)

pub trait Concat<Item>

where
    Item: ?Sized,

{
    type Output;

    // Required method
    fn concat(slice: &Self) -> Self::Output;
}

🔬This is a nightly-only experimental API. (slice_concat_trait #27747)

Expand description

Helper trait for [T]::concat.

Note: the Item type parameter is not used in this trait, but it allows impls to be more generic. Without it, we get this error:

error[E0207]: the type parameter `T` is not constrained by the impl trait, self type, or predica
   --> library/alloc/src/slice.rs:608:6
    |
608 | impl<T: Clone, V: Borrow<[T]>> Concat for [V] {
    |      ^ unconstrained type parameter

This is because there could exist V types with multiple Borrow<[_]> impls, such that multiple T types would apply:

pub struct Foo(Vec<u32>, Vec<String>);

impl std::borrow::Borrow<[u32]> for Foo {
    fn borrow(&self) -> &[u32] { &self.0 }
}

impl std::borrow::Borrow<[String]> for Foo {
    fn borrow(&self) -> &[String] { &self.1 }
}

Source

🔬This is a nightly-only experimental API. (slice_concat_trait #27747)

The resulting type after concatenation

Source

🔬This is a nightly-only experimental API. (slice_concat_trait #27747)

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.

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Note: str in Concat<str> is not meaningful here. This type parameter of the trait only exists to enable another impl.

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