Re: Why can't I do for...in on a table?

[Chris Marrin <chris@...>]

Mike Pall wrote:
> ...
> No surprises here -- more functionality comes at a price.
>
> Caveat: this is a micro benchmark that measures only one tiny
> aspect of the whole implementation. Overall Lua 5 is faster
> than Lua 4.
>
> Note that putting the plain table syntax back into Lua 5.1
> would not be faster (the call overhead is still there).
>
> The only realistic way to get back the Lua 4 speed is to
> add a new syntax (which allows the lexer to distinguish the
> two cases) and a new opcode. I'm not sure this pays off
> when not doing micro benchmarks.

Syntax could look like this (riffing off of recent posts):

    for p from t do ... end

Here, t must either be a table or a userdata with a __iter() metamethod, 
allowing the great additional feature of being able to iterate userdatas!

--
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