Zhao_Xin
(Zhao Xin)
1
I got this by discussions in another thread of swift-evolution. The result
is interesting. I don't know if it should be treat as a bug.
protocol Good {
func printSomething(something:String)
}
extension Good {
func printSomething() { self.printSomething("Good") }
}
struct Name:Good {
func printSomething(something: String = "John") {
print(something)
}
}
struct Talk:Good {
func printSomething(something: String = "Hahaha") {
print(something)
}
}
var protocols:[Good] = [Name(), Talk()]
for p in protocols {
p.printSomething() // Good, Good instead of John, Hahaha
}
As you can see, the final result is "Good, Good", not as I expected "John,
Hahaha", is that right or is it a bug?
zhaoxin
Tino
(Tino)
2
is that right or is it a bug?
It's not a real bug, but I'd call it "unexpected behavior" — and I guess it will be changed sooner or later.
In the meantime: When you include the extension method in the protocol, everything should be fine.
Tino
GregLeszek
(Grzegorz Leszek)
3
This is expected behavior.
for p in protocols {
p.printSomething() // Good, Good instead of John, Hahaha
}
is calling method from extension:
extension Good {
func printSomething() { self.printSomething("Good") }
}
this method (for class Name) is calling method guaranteed by protocol :
func printSomething(something: String = "John") {
print(something)
}
and this method is printing Good, because it has a argument. (Default
Parameter Value - John - is not triggered)
More about it:
* video "Protocol-Oriented Programming in Swift" (WWDC 2015 - Session 408)
* Swift Book, section Function, subsection Default Parameter Values
Greg
···
2016-01-16 12:51 GMT+00:00 肇鑫 via swift-evolution <swift-evolution@swift.org>:
I got this by discussions in another thread of swift-evolution. The result
is interesting. I don't know if it should be treat as a bug.
protocol Good {
func printSomething(something:String)
}
extension Good {
func printSomething() { self.printSomething("Good") }
}
struct Name:Good {
func printSomething(something: String = "John") {
print(something)
}
}
struct Talk:Good {
func printSomething(something: String = "Hahaha") {
print(something)
}
}
var protocols:[Good] = [Name(), Talk()]
for p in protocols {
p.printSomething() // Good, Good instead of John, Hahaha
}
As you can see, the final result is "Good, Good", not as I expected "John,
Hahaha", is that right or is it a bug?
zhaoxin
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swift-evolution@swift.org
https://lists.swift.org/mailman/listinfo/swift-evolution
cryo
(Sune Foldager)
4
Isn’t is just because “equivalent modulo default parameters” ranks lower in overload resolution? That may or may not be on purpose or desired, I don’t really know. As long as it’s documented, I guess.
-Sune
···
On 16 Jan 2016, at 16:06, Tino Heth via swift-evolution <swift-evolution@swift.org> wrote:
is that right or is it a bug?
It's not a real bug, but I'd call it "unexpected behavior" — and I guess it will be changed sooner or later.
In the meantime: When you include the extension method in the protocol, everything should be fine.
Tino
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swift-evolution mailing list
swift-evolution@swift.org
https://lists.swift.org/mailman/listinfo/swift-evolution
