Finds the nested data structure type from a Game Maker map.

ds_map_get_type.gml

/// @desc Returns the type of data structure nested at a key of a ds_map.
/// @param id {Integer} The id of the ds_map to consider.
/// @param key {String} The key of the ds_map to inspect.
/// @author Kat @katsaii
if (is_real(argument0[? argument1])) {
    // copy the ds_map into a duplicate map that can be manipulated freely
    var clone = ds_map_create();
    ds_map_copy(clone, argument0);
    // delete all records other than what's required
    var key = ds_map_find_first(clone);
    repeat (ds_map_size(clone)) {
        var key_next = ds_map_find_next(json_map,json_map_key);
        if (key != argument1) {
            clone[? key] = noone;
            /* This prevents nested structures from being deleted when we remove
             * the record from the cloned map.
             */
            ds_map_delete(clone, key);
        }
        key = key_next;
    }
    // encode the final json and free dynamic structures
    var context = json_encode(clone);
    clone[? argument1] = noone; // see above
    ds_map_destroy(clone);
    // actual inspection occurs here
    context = string_replace(context, "\"" + string(argument1) + "\"", "");
    var trim_start = string_pos(":", context) + 2;
    var trim_end = string_length(context) - 1;
    var trimmed = string_copy(context,
            trim_start,
            trim_end - trim_start);
    switch (string_char_at(trimmed, 1)) {
    // the first character is enough information to infer the type of structure
    case "[":
        return ds_type_list;
        break;
    case "{":
        return ds_type_map;
        break;
    }
}
// if the key is not real, there is no chance of it being a data structure
return -1;