Comment by ben_w

Similar.

Compiler error while working on some ObjC. Nothing obviously wrong. Copy-pasted the line, same thing on the copy. Typed it out again, no issue with the re-typed version. Put the error version and the ok version next to each other, apparently identical.

I ended up discovering I'd accidentally lent on the option key while pressing the "-"; Monospace font, Xcode, m-dash and minus looked identical.