Cast empty Vec<&'a T> to Vec<&'static T>

alice · November 1, 2021, 9:17am

Because the vector has zero elements.

nanoqsh · November 1, 2021, 9:19am

Oh, exactly. Now it's all clear

scottmcm · November 1, 2021, 9:23am

If you're curious, this one is the library doing a bunch of work to detect the cases, with things like

rust-lang/rust/blob/ff0e14829e1806ca0d4226595f7fdf3e8658758f/library/alloc/src/vec/source_iter_marker.rs#L7-L10


      
          /// Specialization marker for collecting an iterator pipeline into a Vec while reusing the
          /// source allocation, i.e. executing the pipeline in place.
          #[rustc_unsafe_specialization_marker]
          pub(super) trait InPlaceIterableMarker {}

Because it was just cleared, so it's never actually called.

(Hyeonu used &42 because that makes the types work out more directly, but it wasn't called either. unreachable!() is -> !, so it can coerce to anything.)

Cyborus04 · November 1, 2021, 9:27am

Hence "unreachable"

That is so awesome, thank you!

system · January 30, 2022, 9:28am

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