Static rustc_lint_defs::builtin::EXPLICIT_OUTLIVES_REQUIREMENTS

pub static EXPLICIT_OUTLIVES_REQUIREMENTS: &Lint

The explicit_outlives_requirements lint detects unnecessary lifetime bounds that can be inferred.

Example

#![deny(explicit_outlives_requirements)]
#![deny(warnings)]

struct SharedRef<'a, T>
where
    T: 'a,
{
    data: &'a T,
}

{{produces}}

Explanation

If a struct contains a reference, such as &'a T, the compiler requires that T outlives the lifetime 'a. This historically required writing an explicit lifetime bound to indicate this requirement. However, this can be overly explicit, causing clutter and unnecessary complexity. The language was changed to automatically infer the bound if it is not specified. Specifically, if the struct contains a reference, directly or indirectly, to T with lifetime 'x, then it will infer that T: 'x is a requirement.

This lint is “allow” by default because it can be noisy for existing code that already had these requirements. This is a stylistic choice, as it is still valid to explicitly state the bound. It also has some false positives that can cause confusion.

See RFC 2093 for more details.