Lua vs Cpp

Differences Lua API vs. C++ API

In general there are the following differences between Lua API and C++ API (assuming you did a local fl = require( "fltk4lua" ) at the top of your Lua source file):

• The prefixes of classes and functions have been removed, so use
  • fl.message() instead of fl_message()
  • fl.run() instead of Fl::run()
  • fl.Box() instead of new Fl_Box()
  • fl.ALIGN_CENTER instead of FL_ALIGN_CENTER (but see below).
• Some enums or preprocessor macros are translated to strings:
  • "FL_UP_BOX" instead of FL_UP_BOX.
• The remaining enums/macros are available as userdata, so that you can combine them using bitwise operators (in Lua 5.3) or the following alternative operators:
  • local a = fl.ALIGN_TOP + fl.ALIGN_LEFT instead of Fl_Align a = FL_ALIGN_TOP | FL_ALIGN_LEFT;
  • local a = b - fl.ALIGN_LEFT instead of Fl_Align a = b & (~FL_ALIGN_LEFT); and
  • if a( fl.ALIGN_TOP ) then instead of if( a & FL_ALIGN_TOP ) (more specifically it's !(~a & FL_ALIGN_TOP), but that only matters when multiple bits are set in the right-hand-side).
• C++ method calls are translated to Lua properties whenever possible, so use
  • b.box = "FL_UP_BOX" instead of b->box( FL_UP_BOX ); and
  • local bt = b.box instead of Fl_Boxtype bt = b->box();.
• Integers used as boolean values are translated to real booleans.
• nil is translated to NULL if NULL is allowed (and vice versa).
• Output parameters end up as (multiple) return values.
• The menu interface is a bit different, though, as it is completely index based, and the Fl_Menu_Items are not exposed as userdata. Instead there are extra methods on the widget that contains the menu items.