Openscad - conditional load of configuration

Question

I have a common design part in OpenSCAD defined by ca. 15 parameters. Is there a way how to put them to configuration files (or something similar) and choose between them conditionally?

I am looking for something like

type = "wide";

if (type == "narrow")
  include <narrow.scad>;
else if (type == "wide">
  include <wide.scad>;
else
  include <round.scad>;

With file wide.scad containing data like

width = 200;
height = 50;
radius = 7;

etc.

I would like to provide the type parameter from commandline, which is possible via -D, but I cannot find a way how to bind the definition to parameter value.

Answer 1

I don't know of a way to put configurations into separate files, but I have solved a similar problems by putting configurations in a table of key-value pairs like this:

// Rows must be in "asciibetical" order by name.
configs = [
  // name     width  height  radius
  ["narrow", [   50,     50,      7]],
  ["round",  [  100,    100,    100]]
  ["wide",   [  200,     50,      7]],
];

A couple helper functions can find the configuration you want from a table of key-value pairs.

function find_row(key, table, low, high) =
  low > high ? undef :
  let(i = round_up(mid(low, high)))
    table[i][0] == key ? table[i][1] :
    table[i][0] <  key ? find_row(key, table, i+1, high) :
                         find_row(key, table, low, i-1);

function find_config(key) =
    find_row(key, configs, 0, len(configs) - 1);

To get a configuration:

config = find_config("wide");
assert(!is_undef(config));

Of course, you have to know which parameter is at which index in the configuration. Usually, I immediately unpack them into variables to given them meaningful names.

width  = config[0];
height = config[1];
radius = config[2];

This works well enough once you've nailed down the parameters that will be part of a configuration. If the code you're writing it still evolving, it can become tedious to make sure you're using consistent indexes.