[swift-evolution] Why doesn't removeLast() on Collection return an optional?

[Max Moiseev]

You can use popLast, that does exactly that: https://github.com/apple/swift/blob/master/stdlib/public/core/BidirectionalCollection.swift#L213 <https://github.com/apple/swift/blob/master/stdlib/public/core/BidirectionalCollection.swift#L213>

Max

> On Oct 17, 2016, at 1:14 PM, Louis D'hauwe via swift-evolution <swift-evolution at swift.org> wrote:
> 
> Regarding the removeLast() function on Collection:
> 
> The current implementation <https://github.com/apple/swift/blob/c3b7709a7c4789f1ad7249d357f69509fb8be731/stdlib/public/core/BidirectionalCollection.swift#L228> is:
> @discardableResult
> public mutating func removeLast() -> Iterator.Element {
>  	let element = last!
> 	self = self[startIndex..<index(before: endIndex)]
> 	return element
> }
> 
> This makes it so that if you call removeLast() on an empty collection you get a fatal error.
> ("fatal error: can't remove last element from an empty collection")
> 
> The documentation for removeLast() <https://github.com/apple/swift/blob/c3b7709a7c4789f1ad7249d357f69509fb8be731/stdlib/public/core/BidirectionalCollection.swift#L220> even has this noted:
> "The collection must not be empty.".
> 
> Surely you could just remove the explicit unwrapping of 'last' and add a guard statement? 
> 
> As such:
> @discardableResult
> public mutating func removeLast() -> Iterator.Element? {
>  	guard let element = last else {
> 		return nil
> 	}
> 	self = self[startIndex..<index(before: endIndex)]
> 	return element
> }
> 
> It sure seems more "Swifty" to alert at compile time that removing the last item of a collection might fail, and make it return nil as a result.
> 
> – Louis D'hauwe
> 
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