[r+] Add enum discriminants to the reference. #21047
Conversation
|
(rust_highfive has picked a reviewer for you, use r? to override) |
| @@ -1413,6 +1413,21 @@ a = Animal::Cat { name: "Spotty".to_string(), weight: 2.7 }; | |||
| In this example, `Cat` is a _struct-like enum variant_, | |||
| whereas `Dog` is simply called an enum variant. | |||
|
|
|||
| Enums can have a discriminator: | |||
There was a problem hiding this comment.
Enums always have a discriminant, this syntax just lets you specify exactly what it is. They'll default to 0, 1, 2, ...
|
@sfackler addressed |
| If a discriminant isn't assigned, they start at zero, and add one for each | ||
| variant, in order. | ||
|
|
||
| You can cast an enum to get this value: |
There was a problem hiding this comment.
One last nit: you can only do this if the enum is C-like, i.e. none of the variants have any data attached. For example, you can't do None as u32.
There was a problem hiding this comment.
C-like, i.e. none of the variants have any data attached.
By "C-like" you mean none like Foo(i32), yes? They all need to be Foo?
There was a problem hiding this comment.
Yep! PR #20907 adds an intrinsic to extract he discriminant from any enum, but its only intended to be used as an optimization for things like PartialEq implementations.
|
r+ with @sfackler 's nit addressed |
nikomatsakis
changed the title
nikomatsakis
changed the title
[r+] Add enum discriminants to the reference. Reviewed-by: nikomatsakis
[r+] Add enum discriminants to the reference. Reviewed-by: nikomatsakis
|
Doing this manually as part of #21300 |
Fixes #15755