I think the best solution is overloading the existing ?? operator. It is very
easy to do:
func ??<T,U: Error>(lhs: T?, rhs: U) throws -> T {
if let lhs = lhs { return lhs } else { throw rhs }
}
then you can say:
do {
let y = try x ?? myError
} catch ...
It might even make sense to add to the standard library.
> On Feb 9, 2017, at 12:04 AM, Jack Newcombe via swift-evolution
> <[email protected]> wrote:
>
> This can actually be accomplished now using a closure:
>
> let value = optionalValue ?? { throw CustomError.failure }()
>
> However, this adds a layer of indirection that I’m not keen on and lacks the
> readability and maintainability of a well-defined operator.
>
> The problem with changing the nil-coalescing operator is that it means
> allowing the second operand to be a statement rather than an expression,
> which I assume would be seen as an unacceptable.
>
>> On 9 Feb 2017, at 07:56, Brent Royal-Gordon <[email protected]> wrote:
>>
>>> On Feb 8, 2017, at 12:00 PM, Jack Newcombe via swift-evolution
>>> <[email protected]> wrote:
>>>
>>> I propose the introduction of a nil-rejection operator (represented here as
>>> !!) as a complement to the above operators.
>>> .
>>> This operator should allow an equivalent behaviour to the forced unwrapping
>>> of a variable, but with the provision of an error to throw in place of
>>> throwing a fatal error.
>>>
>>> - value !! Error :
>>> if value is nil, throw non-fatal error
>>> if value is not nil, return value
>>>
>>> Example of how this syntax might work (Where CustomError: Error):
>>>
>>> let value = try optionalValue !! CustomError.failure
>>
>> Rather than invent a new operator, I'd prefer to make `throw` an expression
>> rather than a statement. Then you could write:
>>
>> let value = optionalValue ?? throw CustomError.Failure
>>
>> One issue here would be figuring out the proper return type for `throw`.
>> Although if `Never` were a subtype-of-all-types, that would of course work.
>> :^)
>>
>> --
>> Brent Royal-Gordon
>> Architechies
>>
>
> _______________________________________________
> swift-evolution mailing list
> [email protected]
> https://lists.swift.org/mailman/listinfo/swift-evolution
_______________________________________________
swift-evolution mailing list
[email protected]
https://lists.swift.org/mailman/listinfo/swift-evolution
