class operator tonumber

I have a class that uses boost::varient to hold any integer, floating
point, or string value. In order to allow lua to easily handle this I
would like to override the lua tostring and tonumber operators to
return the correct type. Something like:

"1.45" = tostring(my_variant)
1.45 = tonumber(my_variant)

I believe that there is a way to do the tostring override using
Luabind, but I have not been able to find anything about tonumber. Is
it possible to override these operators?

Thanks,
Aron

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