How to call a library function by its name and setting it's parameters

Question

I have a library functions defined like that in my C code :

static const struct luaL_reg SelSurfaceLib [] = {
    {"CapabilityConst", CapabilityConst},
    {"create", createsurface},
    {NULL, NULL}
};

static const struct luaL_reg SelSurfaceM [] = {
    {"Release", SurfaceRelease},
    {"GetPosition", SurfaceGetPosition},
    {"clone", SurfaceClone},
    {"restore", SurfaceRestore},
    {NULL, NULL}
};

void _include_SelSurface( lua_State *L ){
    luaL_newmetatable(L, "SelSurface");
    lua_pushstring(L, "__index");
    lua_pushvalue(L, -2);
    lua_settable(L, -3);    /* metatable.__index = metatable */
    luaL_register(L, NULL, SelSurfaceM);
    luaL_register(L,"SelSurface", SelSurfaceLib);
}

And I can use it with this Lua code :

local sub = SelSurface.create()
local x,y = sub:GetPosition()
...

Now, my difficult issue : I'm using follwing code

function HLSubSurface(parent_surface, x,y,sx,sy )
    local self = {}

    -- fields
    local srf = parent_surface:SubSurface( x,y, sx,sy )

    -- methods
    local meta = {
        __index = function (t,k)
            local tbl = getmetatable(srf)
            return tbl[k]
        end
    }
    setmetatable( self, meta )

    return self
end

and my main code is :

sub = HLSubSurface( parent, 0,0, 160,320 )
x,y = sub.GetPosition()

but it's failing

./HDB/80_LeftBar.lua:19: bad argument #1 to 'SetFont' (SelSurface expected, got userdata)

It's because I need to provide srf as 1st argument to GetPosition() function ... but I strictly duno how to do that :(

I don't want to do it when calling GetPosition(), x,y = sub.GetPosition() but I'm looking for a way to do it transparently by setting it in meta's function.

In other words, I would like to have HLSubSurface object to inherit methods from SubSurface.

Any idea ?

Thanks.

Laurent

To be clear, you want the call `sub.somemethod(..)` to turn into `srf:somemethod(...)` behind the scenes where, with `srf` being whatever it was set to when it was created with `HLSubSurface`? — greatwolf, Jan 27 '17 at 00:53

Egor Skriptunoff · Answer 1 · 2017-01-27T14:32:27.517

1

function HLSubSurface(parent_surface, x, y, sx, sy)
   local srf = parent_surface:SubSurface(x, y, sx, sy)

   local self = {
      -- fields
      ....
   }

   setmetatable(self, {__index = 
      function (obj, key)
         local parent_field
         local parent_fields = getmetatable(srf).__index
         if type(parent_fields) == "function" then
            parent_field = parent_fields(key)
         elseif parent_fields then 
            parent_field = parent_fields[key]
         end
         if type(parent_field) == "function" then
            return 
               function(o, ...)
                  if o == obj then
                     return parent_field(srf, ...)
                  else
                     return parent_field(o, ...)
                  end
               end
         else
            return parent_field
         end
      end
   })

   return self
end

And your main code would be:

sub = HLSubSurface( parent, 0,0, 160,320 )
x,y = sub:GetPosition()

edited Jan 27 '17 at 14:32

answered Jan 27 '17 at 08:50

Egor Skriptunoff

906
1
8
23

Thanks for your reply, but I would like to avoid to redeclare all function I have in my library (there are dozens :) ). Is any way to pass the function name as argument and call something like obj.srf:$funcname() ? – destroyedlolo Jan 27 '17 at 14:03
@destroyedlolo - Answer updated. All parent functions are inherited with auto-replacement of their first argument. – Egor Skriptunoff Jan 27 '17 at 14:34
Ok, I'm out for 1 week, but at my return, I will test and feedback. Thanks again. – destroyedlolo Jan 27 '17 at 16:05
How would you survive whole week without programming? – Egor Skriptunoff Jan 27 '17 at 17:29

How to call a library function by its name and setting it's parameters

1 Answers1