A bool or enum by any other name:

Toggles in functions

by Andrzej Krzemieński

From the article:

Have you ever seen a function call like this?

process(true, false);

We are processing something: this should be clear from the context. But what do these parameters mean? What is true and what is false? From the function call we will never figure it out. The code surely isn’t self explanatory.

We will have to stop, and take a look at the declaration, and it does give us a hint:

void process(bool withValidation,
             bool withNewEngine);

Apparently, the author of the function uses the two bools as toggles...