FTA: “I'm especially proud of my little prompt macro“ I don’t understand why that has to be a macro. It asks for user input, so “because it has to be fast” can

FTA: “I'm especially proud of my little prompt macro“ I don’t understand why that has to be a macro. It asks for user input, so “because it has to be fast” can’t be the answer, can it? I also don’t think it avoids some allocations. It’s creating two String’s, one for the call to read_line, and one to convert its trimmed result back to a String, is it? What do I overlook?