Documenting binding syntax for pattern matching

[ghost]

Ref #7173.

[ghost]

A couple of things:

• I'm not a fan of the description I've given of this syntax, it doesn't flow very well. Improvements are much desired.
• Should something be written for the manual as well?
• Are there instructions around for updating doc/po/tutorial.md.pot?

[huonw]

Could you write this as c @ (a, b) (just stylistic; and do it below too). Also, writing the a and b prints as {} rather than {:?} would be nicer.

[huonw]

I think this might be clearer (or would at least benefit from) having a subpattern as-pattern. i.e.

let x: Option<(u8, i16)> = foo();
match x {
    Some(tuple @ (a, b)) => { ... }
    None => { ... }
}

(Also, note that Haskell calls these "as patterns", and I personally don't see a reason to depart from this nomenclature; others might have a better name though.)

[huonw]

It would be good to not have unused variables like b here, and a, b in the example below. For this one, replacing it with _ would be ok, for the one below, maybe print them as well as the entire tuple?

[emberian]

Closing due to inactivity; feel free to reopen!