///button_plusminus_shortcut(button, pressed?)

var button = argument0;
var pressed = argument1;

if (instance_exists(obj_lock))
{
    switch(button)
    {
        case but.plus:  var hold = obj_lock.plus;  break;
        case but.minus: var hold = obj_lock.minus; break;
        
        default:
            show_debug_message("ERROR: Wrong parameter assignment.");
            return;
        break;
    }
    
    hold.hover = true;
    hold.pressed = pressed;
    
    if (pressed)
        with (hold)
            button_do(type);
}