Re: Gotchas in math metamethods etc

[Leo Razoumov <slonik.az@...>]

On Sun, Mar 13, 2011 at 00:15, HyperHacker <hyperhacker@gmail.com> wrote:
> Something I stubbed my toe on the other day:
>> obj={val=2}
>> meta={}
>> function meta:__mul(num) return self.val * num end
>> setmetatable(obj, meta)
>> =obj*4
> 8
>> =4*obj
> stdin:1: attempt to index local 'self' (a number value)
> stack traceback:
>        stdin:1: in function <stdin:1>
>        stdin:1: in main chunk
>        [C]: ?

You expect that "__mul" is symmetric to its arguments which is not the
case in Lua. You can achieve the desired behavior by slightly
modifying your code.

-- Untested:
function meta:__mul(num)
    if type(self) == 'number' then self,num = num,self end
    return self.val * num
end


--Leo--