Re: Make sure numbers are numbers

[Henk Boom <henk@...>]

On 19 April 2010 00:06, HyperHacker <hyperhacker@gmail.com> wrote:
> The solution to that is to copy it:
> lua_pushvalue(L, someindex);
> n = lua_tonumber(L, -1);
> lua_pop(L, 1);
> You can define C preprocessor macros for this, but they get a little
> hairy for the fact that macros can't return a value. Better to use a
> function.

Aside from the fact that lua_tonumber doesn't actually change the
stack, and that it IS actually better to use a function, why couldn't
the comma operator be used for this?

http://en.wikipedia.org/wiki/Comma_operator

Something like this (let me know if I'm wrong):

lua_Number COPY_TONUMBER__n;

#define COPY_TONUMBER(L, index) ( \
    lua_pushvalue(L, index), \
    COPY_TONUMBER__n = lua_tonumber(), \
    lua_pop(L, 1), \
    COPY_TONUMBER__n \
)

..
lua_Number n = COPY_TONUMBER(L, 1);
..

    henk