String equality?

[Chris Marrin <chris@...>]

I may have asked this before, but the issue has come up again, so I 
apologize if it is redundant.

If I write an __index() metamethod in C, it will get called with a 
string parameter, so:

    local a = obj.foo

If obj has an __index metamethod, I can go like this in that metamethod:

    const char* prop = lua_tostring(L, -1);

and I will have a pointer to "foo". Now if I go:

    lua_pushstring(L, "foo");
    const char* s = lua_tostring(L, -1);

will the pointer s always be equal to the pointer prop? In all the cases 
I have tried it is. But can I rely on this?

This comes up because I want to make an atom table. For instance, I want 
to do something like this to create the atom:

    lua_getfield(L, LUA_GLOBALSINDEX, "__atomtable");
    lua_pushlightuserdata(L, lua_tostring(L, -1));
    lua_setfield(L, -2, "foo");

And I will store the string pointer as the value of the atom. Now I want 
to go:

    if (lua_tostring(L, -1) == myFooAtom) // the strings match!

As I said, this works today in test cases I have written. But can I 
reliably use this as an efficient atom mechanism? If not, is there any 
way I can test strings coming in from the Lua stack without interning a 
test string every time?

--
chris marrin              ,""$, "As a general rule,don't solve puzzles
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