Mapping booleans to Option

[jonhoo]

In a decent number of situations, I end up finding myself writing code like:

if foo {
    Some(bar)
} else {
    None
}

This happens especially in closures passed to Iterator::filter_map, but I also frequently find that I want this in .and_then (e.g., on futures). For cases like these, it'd be very handy to have a concise way of turning booleans into Options. For example:

impl bool {
    fn map_true<T>(&self, on_true: T) -> Option<T> { if *self { Some(on_true) } else { None }}
    fn map_false<T>(&self, on_true: T) -> Option<T> { if *self { None } else { Some(on_true) }}
}

There could also be closure variants of this for cases where the T is expensive to construct, but in my experience those cases are rarer. That would let the code above become:

foo.map_true(bar)

The name could of course be bikeshed (if_true?), but I think this is a pretty versatile and useful shorthand!

[Reconcyl]

Are you looking for Option::filter()? It's currently unstable so you can only use it with #[feature(option_filter)] on nightly, but it seems like it's what you want.

[killercup]

You could probably use boolinator to write foo.as_some(bar)

[varkor]

For what it's worth, I've seen this question come up multiple times in the past (and I know I've made use of the pattern before). Perhaps it is worth considering adding it to bool's implementation.

Edit: Ah, I knew I had seen it recently. I forgot it was in the RFCs repository rather than this one.

[kennytm]

Please check rust-lang/rfcs#2180.

[jonhoo]

@ScratchMan544 Option::filter isn't quite the same, as it is Option<T> -> bool -> Option<T>, whereas what I want is bool -> T -> Option<T>. The RFC @kennytm links is exactly this (though I think it should also have a variant for false)! I guess I'll close in favor of that.