// collision list will be a ds_list holding instance ids, or noone
var radius = sprite_get_width(sprite_index) / 2; // assumes object is circular
var collision_list = scr_collision_circle_list(x, y, radius, obj_collidables, true, true);

// check list isn't empty
if (collision_list != noone) {

    // iterate through the list
    for (var n = 0; n < ds_list_size(collision_list); n++) { // all objects that can collide should have a common parent object

            var inst = ds_list_find_value(collision_list, n);

            // get direction to instance
            var dir = point_direction(x, y, inst.x, inst.y);

            // only bounce the object if it hasn't already been bounced
            if (inst.direction != dir( {
                inst.speed *= speed_multiplier;
                inst.direction = dir;
            }
    }

    // clean up ds objects when you're done with them, else they sit in memory even when their pointer is a local var
    ds_list_destroy(collision_list);

}