[swift-evolution] Nil-rejection operator

Jack Newcombe jack at newcombe.io
Thu Feb 9 02:04:15 CST 2017

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 <brent at architechies.com> wrote:
>> On Feb 8, 2017, at 12:00 PM, Jack Newcombe via swift-evolution <swift-evolution at swift.org> 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

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