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 > <swift-evolution@swift.org> 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 <br...@architechies.com> wrote: >> >>> On Feb 8, 2017, at 12:00 PM, Jack Newcombe via swift-evolution >>> <swift-evolution@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 >> > > _______________________________________________ > swift-evolution mailing list > swift-evolution@swift.org > https://lists.swift.org/mailman/listinfo/swift-evolution
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