Argument labels are a core feature of Swift, and let us write code like this:
for i in 1.stride(through: 9, by: 2) {
print(i)
}
Without the through
or by
labels, this code would lose its self-documenting nature: what do the 9 and 2 do in 1.stride(9, 2)
? In this example, Swift also uses the argument labels to distinguish 1.stride(through: 9, by: 2)
from 1.stride(to: 9, by: 2)
, which produces different results.
As of Swift 2.2, you can now use a variety of language keywords as these argument labels. You might wonder why this would be a good thing, but consider this code:
func printGreeting(name: String, repeat repeatCount: Int) {
for _ in 0 ..< repeatCount {
print(name)
}
}
printGreeting("Taylor", repeat: 5)
That uses repeat
as an argument label, which makes sense because the function will print a string a number of times. Because repeat
is a keyword, this code would not work before Swift 2.2 – you would need to write repeat
instead, which is unpleasant.
Note that there are still some keywords that may not be used, specifically var
, let
and inout
.
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