Using if with difference in openSCAD - openscad

Question

I want to create a model in openSCAD
and then I want to cut optionally cut a hole into it (Using difference)
so I can do something like
module model_with_hole( hole=false) {
difference() {
//the_model()
if (hole) {
//the_hole()
}
}
}
But this is actually saying something like "always cut something out of the model except that what you cut might be nothing if a hole is not required".
another alternative would be:
module model_with_hole( hole=false) {
if (hole) {
difference() {
//the_model()
//the_hole()
}
}
else {
//the_model()
}
}
But this is actually saying something like "if you need a hole then render the model and remove the hole, otherwise just render the model".
Is there a way to code this such that the call to render the model would only exist once and the difference action would only happen if required?
if (hole) {the_hole()} the_model();
So the code would feel more like saying render the model and the if require cut the hole ?

Answer 1

Perhaps this is what you want:
add the parameters of the holes to a vector and use this vector in a for loop in difference(). If the vector is empty, nothing is subtracted from the model, try the four examples:
module model(l) {
cube(size = l, center = true);
}
module hole(pos, dim) {
translate(pos) cylinder(h = dim[0] + 0.1, r = dim[1], center = true);
}
// holes = [];
// holes = [[[0,0,0],[10, 1]]];
holes = [[[-2.5,-2.5,0],[10, 0.5]], [[0,0,0],[10, 1]], [[2.5,2.5,0],[10, 1.5]]];
// holes = [[[-2.5,-2.5,0],[10, 1]], [[-2.5,2.5,0],[10, 1]], [[2.5,2.5,0],[10, 1]], [[2.5,-2.5,0],[10, 1]], [[0,0,0],[10, 1]]];
difference() {
model(10);
for (h = holes) hole(h[0], h[1]);
}