Document the "as _" (as-underscore) syntax for value coercion / type casting

[cher-nov]

I'm pretty sorry if I've somehow missed that somewhere in the official docs.
But that really stumbled me for a hour just now.

This syntax is mentioned there in the opening post, for example:
#45480

[jonas-schievink]

as is documented here: https://doc.rust-lang.org/std/keyword.as.html

It could explicitly mention that the destination type can be an _ placeholder.

[cher-nov]

It could explicitly mention that the destination type can be an _ placeholder.

I think, it would be also nice to clarify similarities and differences between as / From:: and as _ / .into().

[poliorcetics]

@rustbot claim

as / From:: and as _ / .into().

I don't think I understand what you want to say with this part. From and Into are (to me) two halves of the same coin, no ?

[cher-nov]

I don't think I understand what you want to say with this part. From and Into are (to me) two halves of the same coin, no ?

They are. But From:: requires type to be explicitly specified, while .into() inferences it, don't they?
Which is like specifying type in as T and omitting it in as _.