Switch on argument type

Question

Using Open SCAD, I have a module that, like cube(), has a size parameter that can be a single value or a vector of three values. Ultimately, I want a vector of three values.

If the caller passes a single value, I'd like all three values of the vector to be the same. I don't see anything in the language documentation about detecting the type of an argument. So I came up with this hack:

module my_cubelike_thing(size=1) {
  dimensions = concat(size, size, size);
  width  = dimensions[0];
  length = dimensions[1];
  height = dimensions[2];
  // ... use width, length, and height ...
}

When size is a single value, the result of the concat is exactly what I want: three copies of the value.

When size is a three-value vector, the result of the concat is nine-value vector, and my code just ignores the last six values.

It works but only because what I want in the single value case is to replicate the value. Is there a general way to switch on the argument type and do different things depending on that type?

Answer 1

If type of size only can be single value or a vector with 3 values, the type can helpwise be found by the special value undef:

a = [3,5,8];
// a = 5;
if (a[0] == undef) {
    dimensions = concat(a, a, a);
    // do something
    cube(size=dimensions,center=false);
}
else {
    dimensions = a;
    // do something
    cube(size=dimensions,center=false);
}

But assignments are only valid in the scope in which they are defined , documnetation of openscad. So in each subtree much code is needed and i would prefere to validate the type of size in an external script (e.g. python3) and write the openscad-code with the assignment of variables to a file, which can be included in the openscad-file, here my short test-code:

#!/usr/bin/env python3
# -*- coding: utf-8 -*-

import os

# size = 20
size = [20,15,10]

if type(size) == int:
    dimensions = [size, size, size]
elif type(size) == list:
    dimensions = size
else:
    # if other types possible
    pass

with open('variablen.scad', 'w') as wObj:
    for i, v in enumerate(['l', 'w', 'h']):
        wObj.write('{} = {};\n'.format(v, dimensions[i]))

os.system('openscad ./typeDef.scad')

content of variablen.scad:

l = 20;
w = 15;
h = 10;

and typeDef.scad can look like this

include <./variablen.scad>;

module my_cubelike_thing() {
    linear_extrude(height=h, center=false) square(l, w);
}

my_cubelike_thing();