I’d like to pitch the following two language changes. Both of them are
technically possible today if you manually write thunks for the relevant
protocol requirements, but it would be nice if we allowed them to be written
directly:
1) Allow closures to satisfy function requirements in protocols
protocol MyProtocol {
func run(param: Int) -> String
}
struct MyStruct : MyProtocol {
var run : (Int)->String // Satisfies requirement MyProtocol.run
}
Among other things, it would make writing type-erased wrappers in the style of
AnyCollection much easier. The only obvious niggle is that the argument label
wouldn’t be required when invoking the closure directly. The labels have no
type-system significance, but it does make it subtly easier to write less
generic code than you intend do. We could solve this by having code-completion
favour protocol methods in this situation, or simply to require the label when
invoking a closure which implements a known protocol requirement.
2) Allow functions with default parameters to satisfy function requirements in
protocols
protocol Sportsplayer {
func goalsScored() -> Int
}
struct SoccerPlayer: Sportsplayer {
struct GoalType : RawOptionSet {
static let Shot = GoalType(0x1)
static let Volley = GoalType(0x10)
static let Header = GoalType(0x100)
static let Any = GoalType(0x111)
}
// Default value .Any means this conforms to Sportsplayer
func goalsScored(type: GoalType = .Any) {
//...
}
}
struct Footballer: Sportsplayer {
struct GoalType : RawOptionSet {
static let Touchdown = GoalType(0x1)
static let FieldGoal = GoalType(0x10)
static let Any = GoalType(0x11)
}
// Default value .Any means this conforms to Sportsplayer
func goalsScored(type: GoalType = .Any) {
//...
}
}
I often find that I want to add some optional, implementation-specific
parameter to a function which implements a protocol requirement. That’s
currently not possible, and it’s a bit annoying.
- Karl
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