Extensions to the default Lua functions for flexibility through metamethods

util.lua

do -- base function reimplementations
    do _G.rawtype = _G.rawtype or _G.type
        local meta, override
        function _G.type(v)
            local vtype = rawtype(v)
            if vtype ~= "table" and vtype ~= "userdata" then return vtype end
            meta = debug.getmetatable(v)
            if meta then
                override = rawget(meta, "__type")
                if override then
                    if rawtype(override) == "function" then
                        return override(v) or rawtype(v)
                    else
                        return override
                    end
                end
            end
            return rawtype(v)
        end
    end
    do _G.rawtostring = _G.rawtostring or _G.tostring
        -- the default already checks __tostring!
    end
    do _G.rawtonumber = _G.rawtonumber or _G.tonumber
        local meta, override
        function _G.tonumber(v)
            local n = rawtonumber(v)
            if n then return n end -- this optimisation makes it nearly as fast as
                                   -- the original for numbers and strings
            meta = debug.getmetatable(v)
            if meta then
                override = rawget(meta, "__tonumber")
                if override then
                    if rawtype(override) == "function" then
                        return override(v)
                    else
                        return override
                    end
                end
            end
            return rawtonumber(v)
        end
    end
    do _G.rawtobool = _G.rawtobool or _G.tobool or function(v) return v and true or false end
        local meta, override
        function _G.tobool(v)
            if rawtype(v) == "boolean" then return v end
            meta = debug.getmetatable(v)
            if meta then
                override = rawget(meta, "__tobool")
                if override then
                    if rawtype(override) == "function" then
                        return override(v)
                    else
                        return override
                    end
                end
            end
            return v and true or false--rawtobool(v)
        end
    end
    do _G.rawnext = _G.rawnext or _G.next
        local meta, override
        function _G.next(v, k)
            meta = debug.getmetatable(v)
            if meta then
                override = rawget(meta, "__next")
                if override then
                    if rawtype(override) == "function" then
                        return override(v, k)
                    else
                        return override
                    end
                end
            end
            return rawnext(v, k)
        end
    end
    do _G.rawunpack = _G.rawunpack or _G.unpack
        local meta, override
        function _G.unpack(v)
            meta = debug.getmetatable(v)
            if meta then
                override = rawget(meta, "__unpack")
                if override then
                    if rawtype(override) == "function" then
                        return override(v)
                    else
                        return override
                    end
                end
            end
            return rawunpack(v)
        end
    end
end