Have some form of destructing if

[kevina]

Having to constantly write code like this:

alt optional_value {
  some (value)  { do something; }
  _ {/*do nothing*/}
}

Is unnecessary verbose in my opinion, and gets annoying to have to constantly write. I would like to be able to say something like:

if (let some(value) = optional_value) {
  do something;
}

Although it doesn't have to be that exact syntax.

[jckarter]

Could you achieve this with a HOF?

    if_some(optional_value) {|value|
        do something;
    }

[kevina]

For the special case of the option::t type sure, but not as a general mechanism when you only care about checking for one of any number of possible enum values.

[kevina]

Rust does have an if_some function but it oddly named as may.

[graydon]

if let is not the weirdest combination for a single refutable pattern. But I think this is pretty low priority, as it's perfectly achievable with alt already, and only saves 1 line of code.

(To be fair, marijn just added alt check because that same one line -- _ { } -- was irritating him too much.)

[catamorphism]

Macros?

Also, https://mail.mozilla.org/pipermail/rust-dev/2012-April/001636.html may be relevant. The "brace-free" syntax that @pcwalton suggested in that thread may help with this problem.

[kevina]

On Thu, 12 Apr 2012, Tim Chevalier wrote:

Macros?

I am proposing new syntax. As Rust syntax is not at the moment extensible, I do not see how a macro will really help.

Also, https://mail.mozilla.org/pipermail/rust-dev/2012-April/001636.html
may be relevant. The "brace-free" syntax that @pcwalton suggested in
that thread may help with this problem.

I do not see how that can help.

[catamorphism]

I mean that having to write the alt might be slightly less annoying if the braces weren't required. It could potentially fit on one line that way.

[kevina]

Yes it might. But the problem is with the empty default case. I always fell obligated to have some sort of comment in the default case to make it clear that it was meant to be empty. With a destructing if, the intention is clear.

[catamorphism]

Ok. I see how this could be useful, but right now we're generally trying not to add more features. Leaving it open in case anyone else has insight.

[pcwalton]

The right solution here is to implement macros, and then implement your feature on top of that. I'd rather not add features that we then remove later in favor of macros because Rust macros are hard to use right now.