Re: Metatable methods

[Александр Машин <alex.mashin@...>]

21.12.2021 19:37, Spar пишет:
> Make a dummy table with metatable and __pairs metamethod in it, make 
> that metamethod return value A, put value B in dummy table.
> Now call pairs on it and read first value. If __pairs was invoked, you 
> get A, if not regular pairs will return B

Thank you, but that's what I meant by probing. This is my current solution:

--[[

	Redefined pairs and ipairs.

--]]



--[[

	Whether a metamethod exists.

	@param string func Function that is supposed to invoke the metamethod.

	@param ?string method Metamethod to check.

	@return bool True, if the metamethod is supported.

--]]

local function metamethod_supported (func, method)

	return not _G [func] (setmetatable ({ 0 }, { [method or '__' .. func] = 
function (tbl) end }))

end



--[[

	Emulate a metamethod, if it does not exist.

	@param string func Function that is supposed to invoke the metamethod.

	@param ?string method Metamethod to emulate.

	@return function Function redefined to take metamethod into account.

--]]

local function emulate_metamethod (func, method)

	if not metamethod_supported (func, method) then

		local raw = _G [func]

		return function (...)

			local metatable = getmetatable (tbl)

			local metamethod = metatable and metatable [method or '__' .. func]

			-- Do not simplify to return ... and ... or ...:

			if metamethod then

				return metamethod (...)

			else

				return raw (...)

			end

		end

	else

		return _G [func]

	end

end



local pairs, ipairs = emulate_metamethod 'pairs', emulate_metamethod 
'ipairs'

Alexander Mashin