On 21.10.17 02:50, Santiago Gil via swift-users wrote:
I just ran into a bug after a Swift 4 migration where we expected [String] and got [Character] from a flatMap since flatMap will flatten the String since it's now a collection. While I understand why flatMap behaves this way now that string are collections, in testing this I found some weird behaviour...var strArr = ["Hi", "hello"] let result = strArr.flatMap { x in returnx }The type of results ends up being [Character] in the above case. However, adding a print statement changes things.var strArr = ["Hi", "hello"] let result = strArr.flatMap { x in print(x) return x } In this case, result is of type [String] This seems like a bug, or is this expected Swift behaviour?
It looks like the compiler infers the type of the closure in the second example to be (String) -> Optional<String> instead of String -> String.
I don't know why and I definitely find it surprising.
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