macOSだと起きない。
$ echo 'import Foundation; "test".character(at: 0)'|swift -frontend -repl -sdk `xcrun --sdk macosx --show-sdk-path` <REPL Input>:1:20: error: value of type 'String' has no member 'character' import Foundation; "test".character(at: 0) ^~~~~~ ~~~~~~~~~ Swift.String:10:16: note: did you mean 'characters'? public var characters: String.CharacterView { get set } ^ Swift.String:8:16: note: did you mean '_characters'? public var _characters: String._CharacterView { get set } ^