[swift-evolution] Proposal: Improve Import of Scanner APIs into Swift 3

[Oliver Drobnik]

Working on a function for Foundation’s Scanner I stumbled on this LLVM crash: https://bugs.swift.org/browse/SR-3295

This got me thinking about a workaround and I would like to prose this:

When importing Foundation into Swift 3, all 

AutoreleasingUnsafeMutablePointer<T?>?

should instead be exposed as simple:

inout T?

e.g.

open func scanString(_ string: String, into result: AutoreleasingUnsafeMutablePointer<NSString?>?) -> Bool

would become

open func scanString(_ string: String, into result: inout String?) -> Bool


The call would stay exactly the same for normal use cases where you specify a receiving variable:

var string: String?
scanString("=", into: &string)

because inout parameters require a &


for the use case where you don’t require a receiving parameter, a second method without result parameter would be generated:

open func scanString(_ string: String) -> Bool

This is necessary because you cannot specify nil or an immutable value for an inout parameter. 


A fixit/migration would change calls to

scanString(“foo", into result: nil)

into

scanString(“foo")


The normal call with receiving variable would stay the same. But the case without return would become more concise.

What do you think?

kind regards
Oliver Drobnik


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