Proposal: `'<T>` lifetime

[Jules-Bertholet]

@CAD97

This is better handled by unsafe binder types, e.g. element: unsafe<'a> &'a T.

Yes, this is specifically intended as an alternative to that; I link to the unsafe binders HackMD in the post.

@CAD97

Well, not quite, since the function already exists and can be referred to with the parameter explicitly provided.

Yes, this is a limitation, but can be fixed over an edition.

@CAD97

Not quite; a function like fn f<T>() -> T with an output generic type can still get an effectively early-bound lifetime by using '<T>.

Well, yes, that is the point, the lifetime can now be derived from the type, so there is now only one early-bound parameter instead of two.

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Extension

We could extend this feature to allow specifying an list of types, such that the resultant lifetime is outlived by all types in the list:

fn leak<T, U>(b: Box<(T, U)>) -> &'<T, U> mut (T, U) { … }

Lifetimes could also be permitted:

fn leak<'a, T>(b: Box<(&'a i32, T)>) -> &'<'a, T> mut (&'a i32, T) { … }