problem with __eq in metatable

["Brian Segall" <brian_segall@...>]

[Lua 5.1.1]

I'm trying to override the comparison operator for some tables. I'm using 
the C API to provide the metamethod. Some pseudo (Lua) code to show my 
intention:

t1 = {string = "hello"}
t2 = {string = "hello"}
if t1 == t2
   something
end

I would like (t1 == t2) to call my C function, which in this example would 
access the strings stored in each table, and use strcmp to determine if 
they're equal.

Here is what I currently have (in C and Lua). I've stepped into the Lua 
code, and the "__eq" entry is different in the metatables of both tables, 
therefore it doesn't call my C function to compare strings.

C file:
----------------
static const char* KEY = "string";

static int CompareStrings(lua_State* L)
{
	lua_pushstring(L, KEY);
	lua_gettable(L, 1);
	const char* s1 = lua_tostring(L, -1);
	lua_pop(L, 1);

	lua_pushstring(L, KEY);
	lua_gettable(L, 2);
	const char* s2 = lua_tostring(L, -1);
	lua_pop(L, 1);

	lua_pushboolean(L, (int)!stricmp(s1, s2));

	// on stack: boolean
	return 1;
}

static int newstring(lua_State* L)
{
	const char* s = lua_tostring(L, 1);

	// the table to return (T1)
	lua_newtable(L);
	lua_pushstring(L, KEY);
	lua_pushstring(L, s);
	lua_settable(L, -3);

	// the metatable (T2)
	lua_newtable(L);
	lua_pushstring(L, "__eq");
	lua_pushcfunction(L, CompareStrings);
	lua_settable(L, -3);

	// set T1's metatable to T2 (top of stack)
	lua_setmetatable(L, -2);

	// on stack: table (T1)
	return 1;
}

test.lua:
--------------------
a = newstring("hello")
b = newstring("hello")
if a == b then
	print("they are equal")
else
	print("they are not equal")
end


----------------------

It always prints "they are not equal" since my comparison function is not 
being called. luaO_rawequalObj in lobject.c is where the __eq methods are 
determined to be different, and lacking a comparison handler Lua returns 
false.

Thanks for the help.

Brian

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