How do you call a class method with named parameters?

Question

I have a C++ class constructor like:

Motors(int p1=0, int p2=0);

However, when I attempt to instantiate it with named parameters like:

Motors motors(p1=123, p2=456);

the Arduino C/C++ compiler gives me the errors:

src/motors.ino:3: error: ‘p1’ was not declared in this scope
src/motors.ino:3: error: ‘p2’ was not declared in this scope

The compiler doesn't seem to support named parameters and thinks I'm referring to variables. I thought named parameters was a pretty widely supported feature, even in C++. What am I doing wrong?

Answer 1

C++ doesn't support named parameters, and I doubt it ever will.

It has strict calling conventions which mean you couldn't re-order the parameters at call-time without adding an unnecessary layer of data duplication/indirection (which would hurt performance). It would also need a significant change to compiler architecture, as variable/parameter names are usually stripped out long before the linker is invoked.

If you want to achieve a similar effect though, you could use comment blocks instead, e.g.:

Motors motors(/*p1*/ 123, /*p2*/ 456);