[swift-evolution] Make non-void functions @warn_unused_result by default

[Haravikk]

> On 25 Feb 2016, at 05:19, Paul Ossenbruggen via swift-evolution <swift-evolution at swift.org> wrote:
> 
> These lack conciseness. What about the already supported: 
> 
> let _ = ingoreResult()

This could work until we gain some other, general purpose, method to suppress warnings, though it isn’t pretty IMO. For example, if a class’ methods are designed to be chain able then the result isn’t necessary (it’s just self), so in things like loops you could end up having to use let _ an awful lot, like so:

	class Chainable {
		var value = 0
		func add(add:Int) {
			value += add
			return self
		}
	}

	let chainable = Chainable()
	for _ in 0 ..< 10 {
		if getSomeCondition() {
			let _ = chainable.add(5)
		} else {
			let _ = chainable.add(2)
		}
	}

Stupid example, but imagine if there were a few other operations, perhaps handled by other conditionals, then suddenly you end up with a lot of these let _ statements, which is why being able to suppress the warnings in all cases is still desirable.

On the topic of verbosity in the attribute, I don’t think there’s any need to go to four words; the current attribute is @warn_unused_result, and I think that @ignore_unused_result works a direct opposite (i.e- the result being unused is still strange to the compiler, but it chooses not to issue a warning about it). I’m only using snake case because that’s what the current value has, obviously we’ll adjust for whatever the final attribute naming convention turns out to be.
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