While I find the concept interesting, I give a big -1 for using the ‘!’ operator for something else that fatal error.
> Le 8 févr. 2017 à 21:00, Jack Newcombe via swift-evolution > <[email protected]> a écrit : > > Hi all, > > Currently there are a number of different operators for dealing with > optionals that cover most of the use cases. However, I think I’ve identified > a missing complement for the existing operators for optionals. > > Take the following outcomes for interacting with an optional using existing > operators (!, ?, ??). The outcomes of using these are as follows: > > - value? : > if value is nil, do nothing and return nil > if value is not nil, complete the chain by evaluating the rest of the > expression. Return the result of the expression > - value! : > if value is nil, throw.a fatal error. > If value is not nil, complete the chain by evaluating the rest of the > expression. Return the result of the expression > - value ?? default : > if value is nil, return default > if value is not nil, return value > > It seems to me that, if it is possible to coalesce a nil value with a default > value, it should also be possible to reject a nil value a non-fatal error. > > 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 > > It is possible to implement this in Swift 3 with the following declaration: > > infix operator !! : NilCoalescingPrecedence > > func !!<UnwrappedType: Any, ErrorType: Error>(lhs: > Optional<UnwrappedType>, rhs: ErrorType) throws -> UnwrappedType { > guard let unwrappedValue = lhs else { > throw rhs > } > return unwrappedValue > } > > I’ve added further examples including composition with the nil-coalescence > operator here: > https://gist.github.com/jnewc/304bdd2d330131ddb8a1e615ee560d1d > <https://gist.github.com/jnewc/304bdd2d330131ddb8a1e615ee560d1d> > > This would be particularly convenient in cases where a functions expects > significant number of optional to contain non-nil values, without the need to > repeat non-generic guard-let structures with the same else code-block. > > Best regards, > > Jack > > _______________________________________________ > swift-evolution mailing list > [email protected] > https://lists.swift.org/mailman/listinfo/swift-evolution
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