The "wow ow" was intended to be thrown more at the Scala compiler than at the code. I'm sorry if it felt offending. I always have trouble communicating the right thing IRL, and even more so in written form.

The problem with this syntax is that it can be interpreted as calling the postfix method `visitMappings` without argument then creating a new object "in the void" (which can be useful if the constructor has side-effects); instead of calling the infix method `visitMappings` with one argument which is on the following line.
The inference used by scalac for this kind of code is at best non-optimal, and that's why postfix notation has been turned into a language import. But it's still better to avoid trying the compiler.