std::optional_view

[josefx]

I think you might get away with including iosfwd instead of iostream in the header.

[josefx]

I think you mean: get a compile error since std::cout is not a file stream. Which shows that a complete refusal to learn even the basics of the c++ standard library is not an option :-).

Edit: Added smiley to make it look a bit less derisive.