Function core::hint::black_box

1.66.0 (const: unstable) · source ·
pub fn black_box<T>(dummy: T) -> T
Expand description

An identity function that hints to the compiler to be maximally pessimistic about what black_box could do.

Unlike std::convert::identity, a Rust compiler is encouraged to assume that black_box can use dummy in any possible valid way that Rust code is allowed to without introducing undefined behavior in the calling code. This property makes black_box useful for writing code in which certain optimizations are not desired, such as benchmarks.

Note however, that black_box is only (and can only be) provided on a “best-effort” basis. The extent to which it can block optimisations may vary depending upon the platform and code-gen backend used. Programs cannot rely on black_box for correctness in any way.