So, the pitfall below seems to be fairly well-known, as I was able to find
previous references to it on the list:
--
protocol P { func foo() }
struct S: P { func foo() { print("foo") } }
func doSomething<C: CollectionType where C.Generator.Element: P>(c: C) {
for each in c {
each.foo()
}
}
let arr: [P] = [S()]
doSomething(arr) // error: cannot invoke 'doSomething' with an argument list of
type '([P])’
--
And, of course, if we go the opposite way:
--
protocol P { func foo() }
struct S: P { func foo() { print("foo") } }
func doSomething<C: CollectionType where C.Generator.Element == P>(c: C) {
for each in c {
each.foo()
}
}
let arr = [S()]
doSomething(arr) // error: cannot invoke 'doSomething' with an argument list of
type '([S])’
--
My questions are twofold.
1. Is there any workaround to this issue that would let one declare a function
that can take a collection whose element is anything that conforms to P,
whether that be statically typed as P or its actual type, without either
writing two versions of every API that takes a collection (and four versions of
every API that takes two collections, eight versions of every API that takes
three, etc.) or just giving up and accepting an array instead of a collection?
2. Are there any plans by the development team to address this issue?
Thanks,
Charles
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