Document @ binding syntax for pattern matching

[kvanbere]

Pattern matching binding syntax is not intuitive and requires documentation, as evidenced by the original issue below

Original

Sometimes it is desirable to be able to bind the entire pattern matched to a separate variable. Haskell uses @ for this, and it works nicely.

Consider input (1,2) fed into...

match vector {
  c@(a, b) => ...
}

...where c = (1,2), a = 1 and b = 2.

[huonw]

This actually exists now:

rusti> match (1,2) { c@(a,b) => println(fmt!("%? %? %?", a, b, c)) }
1 2 (1, 2)

[kvanbere]

The tutorial lacks documentation on this. Could this ticket represent the task of adding such documentation?

[Aatch]

@kvanberendonck I have edited your issue to be for documentation.

[sanxiyn]

There was a discussion to change this from @ to something else: https://mail.mozilla.org/pipermail/rust-dev/2013-May/003989.html

[emberian]

This still needs doing. Shouldn't be too hard.

[lilyball]

This probably doesn't need doing anymore, since @ is being removed.

[huonw]

@kballard hm? Is the pattern-matching @ being removed?

[lilyball]

@huonw No, I meant @-boxes are going away, so there's no more need for a@@b in match. I suppose I was unclear; I was responding to @sanxiyn's comment and link to the ML suggesting that the match binding syntax should change.

[whatisaphone]

This is now documented in both the tutorial and the manual

http://static.rust-lang.org/doc/master/tutorial.html#pattern-matching
http://static.rust-lang.org/doc/master/rust.html#match-expressions

It can probably be closed.

[alexcrichton]

Thanks for the tip @johnsoft!