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Oh Rust, you be fickle sometimes! Today during a live stream I was exploring a lifetime issue, and I came up with this:

gist.github.comFickle lifetimesFickle lifetimes. GitHub Gist: instantly share code, notes, and snippets.

At an initial glance it seems like both functions should compile, after all the only difference is that we are returning an alias, right? SPOILER AHEAD: So why does the function returning an alias work while the other one doesn't? The answer can be found here: doc.rust-lang.org/reference/li...

doc.rust-lang.orgLifetime elision - The Rust Reference

13/11/25, 6:23 pm0 reposts2 likes

Togglebit

@togglebit.io

13 Nov 2025

In short these two are the same: type T1<'a> = Box<dyn Bar<'a>>; type T2<'a> = Box<dyn Bar<'a> + 'a>; So by returning the type alias we are not returning Box<dyn Trait<'a>> but Box<dyn Trait<'a> + 'a>.