Good idea. I should definitly add built-in support for std::optional.

One thing this would provide is a straight forward way to check if an optional argument was passed or not.

Is there currently a canonical way to do that? I guess I could use .call(...) with some lambda that sets a bool to true, but that seems quite verbose. I was thinking something like:

option("--foo").set_true(foo_passed) & value(foo)

Or a way to get a handle the "option object" and query it after command line parsing, something like foo_option.was_passed().

Is there currently a canonical way to do that?

To answer my own question, according to https://github.com/muellan/clipp#actions I guess you can do:

bool foo_passed = false;
int foo = 0;
option("--foo").set(foo_passed) & value("FOO", foo);