Why does it say where T: Sized for references &T? A reference can definitely point to an unsized type, e.g. &str.
The yellow boxes really mean "must be heap allocated" - all the other references (&T, &[T] and &dyn Trait) may either point to the stack or the heap.

[–] jameseb@lemm.ee 6 points 4 months ago* (last edited 4 months ago)

Why does it say where T: Sized for references &T? A reference can definitely point to an unsized type, e.g. &str.

I think the point being made is that the layout shown only applies for Sized T. Layouts for &[T] and &dyn Trait are shown elsewhere on the sheet. &str is noted under &[T].

Edit: although, similar considerations would apply to other pointer types, but that isn't noted on the sheet except for Box<[T]>

[–] sgued@programming.dev 4 points 4 months ago

Because when T is !Sized, the layout is different, it looks more like the layout of &[T].