metamethods.hpp

Go to the documentation of this file.

#pragma once
#include <meta>
 
#include <welder/bind_traits.hpp> // is_unary_operator

 
namespace welder::inline v0::rods::lua {

consteval const char* lua_metamethod_name(std::meta::info f) {
    using std::meta::operators;
    const bool unary{::welder::detail::is_unary_operator(f)};
    switch (std::meta::operator_of(f)) {
        case operators::op_plus:
            return unary ? nullptr : "__add"; // no unary +
        case operators::op_minus:
            return unary ? "__unm" : "__sub";
        case operators::op_star:
            return unary ? nullptr // unary * is dereference, not a Lua metamethod
                         : "__mul";
        case operators::op_slash:   return "__div";
        case operators::op_percent: return "__mod";
        case operators::op_equals_equals: return "__eq";
        case operators::op_less:          return "__lt";
        case operators::op_less_equals:   return "__le";
        // Lua derives ~=, > and >= from __eq/__lt/__le, so these expose nothing.
        case operators::op_exclamation_equals:
        case operators::op_greater:
        case operators::op_greater_equals: return nullptr;
        case operators::op_parentheses:    return "__call";
        // operator[] -> Lua's __index (a fallback consulted after normal
        // member/method lookup, so it coexists with fields and methods).
        case operators::op_square_brackets: return "__index";
#if defined(LUA_VERSION_NUM) && LUA_VERSION_NUM >= 503
        // Bitwise: Lua 5.3+ only. C++ operator^ is XOR (Lua __bxor), NOT power.
        case operators::op_caret:     return "__bxor";
        case operators::op_tilde:     return unary ? "__bnot" : nullptr;
        case operators::op_ampersand:
            return unary ? nullptr // unary & is address-of
                         : "__band";
        case operators::op_pipe:            return "__bor";
        case operators::op_less_less:       return "__shl";
        case operators::op_greater_greater: return "__shr";
#endif
        default: return nullptr;
    }
}
 
} // namespace welder::rods::lua