Type Metafield

["Leandro Candido" <enclle@...>]

Hello all,

    Well, I don't know if this is already done, but...
    Below is a substitute to function "type" IN LUA SIDE, you can replace
either luaB_type in lbaselib.c or in lua, with the script below. This new
type allow you to add a "type metafield"( __type) to be more descriptive,
for example, instead of print( type(acomplexnum) ) --> userdata, the output
is print( type(acomplexnum) ) --> complex.
    The old "type" function is now "rawtype". How to do in C ( in file
"lbaselib.c" ):

    1) rename luaB_type to luaB_rawtype
    2) Copy this before luaB_rawtype:

static int luaB_type(lua_State*L) {
  luaL_checkany(L,1);
  if( luaL_getmetafield(L,1, "__type" ) == 0) // Get value of __type, 0 ==
no metafield
    lua_pushstring(L, lua_typename(L, lua_type(L,1))); file://"raw" type,
same as luaB_rawtype
  return 1;
}

    3) search for {"type", luaB_type} and add before/after it:
     {"rawtype", luaB_rawtype},

    4) recompile.

How to do in Lua (WITHOUT adding the above in the C side (lbaselib.c)):

Use this block of code:

-- start of block

rawtype = type

type = function ( var )
  local _m = getmetatable(var);
  if _m and _m.__type then
   return _m.__type;
  end
  return rawtype(var);
 end

-- end of block

Script to test C/Lua:

-- start of block

function Window()
 local _w = {}
 local _m = { __type = "window" }
 setmetatable( _w, _m );
 return _w;
end


-- win, here, is a table with metafield __type as "window"
win = Window()

print( rawtype(win) ); --> table
print( type(win) ); --> window

print( "win is a table? ", type(win) == "table" ); --> false
print( "win is a window?", type(win) == "window" ); --> true
print( "But, win is a table?", rawtype(win) == "table" ); --> true
print( "But, win is a window?", rawtype(win) == "window" ); --> false

-- end of block


                                                                        The
God's Peace,


          Leandro.