Parameters of type pair with defaults cause unexpected type errors

[DanielW0108]

Minimal example:

int f (pair foo=(0,0), int x) {
  return x;
}

f(1);

Trying to compile this gives the following error: cannot call 'int f(pair foo=<default>, int x)' with parameter '(int)'

Calling f(x = 1) compiles, as does swapping the order of the parameters to this:

int f (int x, pair foo=(0,0)) {
  return x;
}

f(1);

This seems to happen whenever x has a type that could appear inside a pair. The same type error happens if int is swapped for real, but swapping it for string avoids it:

string f (pair foo=(0,0), string x) {
  return x;
}

f("a");

Casting to a non-pair-y type seems to behave differently to casting to a pair-y type:

• Calling f((string)1) here does compile
• Calling f((int)1) for the int versions does not compile, likewise f((real)1) for the real version

This happens on both the web version (2.86-7) and the latest version available on my repo (2.70)

[johncbowman]

This is the expected behaviour of Asymptote's function signature matching algorithm, as described here:

https://asymptote.sourceforge.io/doc/Default-arguments.html

See also https://asymptote.sourceforge.io/doc/Named-arguments.html

In your example, the int argument can be cast to a pair, and so it assigned to the first argument. You then need to supply a second int since the second argument does not have a default value.

[johncbowman]

Perhaps what you really intended was

int f (explicit pair foo=(0,0), int x) {
  return x;
};

[DanielW0108]

Ah, I wasn't aware that ints can be implicitly cast to pairs - makes sense when treating pairs as complex numbers, but unintuitive when they're mostly being used as coordinates. Thanks for the response.