Re: idea: __iter generic-for metamethod

["Stuart P. Bentley" <stuart@...>]

Going from a post Joonas just made, it should actually read like this:

A for statement like

     for var_1, ···, var_n in explist do block end

is equivalent to the code:

     do
       local f, s, var = explist

       --proposed addition
       if type(f)~= "function" and not metatable(f).__call then
         local meta_f = metatable(f).__iter
         if not meta_f and type(f)=="table" then meta_f = pairs
         if meta_f then f, s, var = meta_f(f) end
       end

       while true do
         local var_1, ···, var_n = f(s, var)
         var = var_1
         if var == nil then break end
         block
       end
     end

(I'd forgotten that __call could be used to replicate the non-factory  
version of __iter.)

On Mon, 24 May 2010 17:06:09 -0700, Stuart P. Bentley  
<stuart@testtrack4.com> wrote:

> On Mon, 24 May 2010 16:53:32 -0700, Jonathan Castello  
> <twisolar@gmail.com> wrote:
>
>
> > I wrote your algorithm into a usable Lua function to try it out. I had
> > to add a check for nonexistent metatables, but it does work.
>
>  From the manual:
>
> "The code shown here in Lua is only illustrative; the real behavior is  
> hard coded in the interpreter and it is much more efficient than this  
> simulation. All functions used in these descriptions (rawget, tonumber,  
> etc.) are described in §5.1. In particular, to retrieve the metamethod  
> of a given object, we use the expression
>
>       metatable(obj)[event]
>
> This should be read as
>
>       rawget(getmetatable(obj) or {}, event)"