std::simd::mask64x4 — Rust type alias

What `mask64x4` does

mask64x4 is a type alias exposed by the std::simd module of the Rust standard library. It is part of the public, stable API and you can rely on it from any edition of Rust.

type mask64x4 = ... introduces a new name for an existing type. The alias is purely a syntactic shortcut — it does not create a distinct type. Use mask64x4 anywhere you would write the underlying type. The full canonical path is std::simd::mask64x4; bring it into scope with use std::simd::mask64x4; or refer to it by its full path.

When to use it

Use mask64x4 as a shorter name for its underlying type. Type aliases do not create new types — they're purely for readability and future-proofing.

Annotated examples

Declaring values of type mask64x4

use std::simd::mask64x4;

fn demo() {
    // mask64x4 is a type alias — it desugars to its underlying type but
    // gives you a meaningful name to read and write. Type aliases do not
    // create new types; they're purely for readability.
    let value: mask64x4 = Default::default();
    let _ = value;
}

Type aliases shorten verbose generic types in your own APIs (e.g. `type Result<T> = std::result::Result<T, MyError>;`) and give domain-specific names to common shapes.

For deeper background, see the canonical Rust patterns reference for the broader context behind this section.

Using mask64x4 in a function signature

use std::simd::mask64x4;

// A type alias makes the function signature self-documenting and lets
// you swap the underlying representation in one place if requirements
// change.
fn process(input: mask64x4) -> mask64x4 {
    input
}

Aliases work in any position a regular type does — function arguments, return values, generic parameters. They're a cheap way to make code more readable.

Common pitfalls

A type alias is not a new type — it does not enforce different semantic intent. If you want the compiler to distinguish two different shapes that share the same underlying representation, use a newtype struct instead.

For deeper background, see an in-depth Rust idioms cheat sheet for the broader context behind this section.

Performance & threading notes

Pure compile-time. The alias is erased before code generation; the resulting binary is identical to one that uses the underlying type directly.

What mask64x4 does