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February 13, 2016 00:31
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Use of "Self" vs "self" in "static var" + generic protocol implementation
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protocol Fooable { | |
static var staticBigSelf: String { get } | |
static var staticSmallSelf: String { get } | |
var instanceBigSelf: String { get } | |
var instanceSmallSelf: String { get } | |
init() | |
} | |
extension Fooable { | |
static var staticBigSelf: String { return String(Self) } | |
static var staticSmallSelf: String { return String(self) } | |
var instanceBigSelf: String { return String(Self) } | |
var instanceSmallSelf: String { return String(self) } | |
} | |
class ParentView: Fooable { | |
required init() {} | |
} | |
class ChildView: ParentView { | |
required init() {} | |
} | |
func fooableFactory<T where T: Fooable>() -> T { | |
print("Creating instance of \(T.self) with Self=\(T.staticBigSelf) & self=\(T.staticSmallSelf)") | |
return T() | |
} | |
func dump<T where T: Fooable>(instance: T) { | |
print("instance \(instance) with Self=\(instance.instanceBigSelf) & self=\(instance.instanceSmallSelf)") | |
} | |
let cv = fooableFactory() as ChildView // Prints: Creating instance of ChildView with Self=ParentView & self=ChildView | |
dump(cv) // Prints: instance ChildView with Self=ChildView & self=ChildView | |
ChildView.staticBigSelf // Prints: "ChildView" | |
ChildView.staticSmallSelf // Prints: "ChildView" |
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What puzzles me is that:
ChildView.staticBigSelf
returnsChildView
, letting us think that theSelf
in thestaticBigSelf
's default implementation is resolved dynamically in this caseT.staticBigSelf
infooableFactory
is always resolved asParentView
even when the genericT
is resolved asChildView
(T.self=ChildView
butT.staticBigSelf=ParentView
) letting us think thatT
andSelf
are resolved statically in this case