> On 17 Jan 2017, at 09:57, David Sweeris via swift-evolution
> <[email protected]> wrote:
>
>
> On Jan 17, 2017, at 03:40, Charlie Monroe via swift-evolution
> <[email protected] <mailto:[email protected]>> wrote:
>
>> I've come across multiple cases, where you simply know the array is never
>> empty and hence the optionality on first, last and behavior of a few other
>> members is slightly different. Also, there are cases where you want to
>> declare that you shouldn't pass an empty array e.g. into an initializer.
>>
>> I was wondering whether Swift could have a specialized NonEmptyArray that
>> could be used throughout the stdlib - e.g. String.components(separatedBy:)
>> would return NonEmptyArray.
>>
>> Thoughts?
>
> I've tried to make such a type a few times... The struct itself isn't hard
> ("var first:T; var tail:[T]"), but I never could figure out how to make
> `NonEmptyArray` conform to `ExpressibleByArrayLiteral` (because the protocol
> doesn't allow for failable inits) without just crashing if there wasn't at
> least one element.
>
> Anyway, I'm not opposed to adding it, as long as there's a non-crashy way to
> assign array literals to them.
Is a failable initialiser the way to go? Could we do something with some kind
of compiler attribute?
For example:
struct MyNonEmptyArray<E> : ExpressibleByArrayLiteral {
typealias Element = E
@minParameters(1) init(arrayLiteral:Element…) { … }
}
In this case the @minParameters attribute tells the compiler how many
parameters must be present in direct calls to this method, however, for cases
where this isn't possible to check it would still trigger a runtime error, but
that would only be for more unusual cases like trying to handle this type as a
generic ExpressibleByArrayLiteral.
Just trying to think whether there might be a more flexible way to do this, as
if you can support arrays with at least 1 element, then why not 2 or 3 etc.? In
the worst case this would just become a runtime error, which is how we would
have to handle right now, but in more common cases the compiler can give an
error right away._______________________________________________
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