Re: ipairs in Lua 5.3.0-alpha
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- Subject: Re: ipairs in Lua 5.3.0-alpha
- From: Ahmed Charles <acharles@...>
- Date: 2014年8月21日 18:30:51 -0700
I'm curious as to why the index metamethod is a fallback when the value does not exist while the len metamethod is not a fallback to the normal length not making sense?
I suppose that would prevent using len on tables at all. Was that the rational?
On Aug 5, 2014, at 3:53 AM, "Luiz Henrique de Figueiredo" <lhf@tecgraf.puc-rio.br> wrote:
>> 3) I wish __call were respected if you give the function type a
>> metatable, and basic C operations were exposed to Lua, like
>> getmetatable(0).__add = <C function to add 2 numbers>
>
> A central point in Lua semantics is that metamethods correspond to
> events that Lua cannot handle. (Metamethods were originally called
> fallbacks, for this reason.) Addition of two numbers is not such an
> event and it is never performed via a metamethod, even if you define one:
>
> Lua 5.2.3 Copyright (C) 1994-2013 Lua.org, PUC-Rio
> > debug.setmetatable(0,{__add=print})
> > a=1
> > b=2
> > =a+b
> 3
> ... but this works:
> > debug.setmetatable(0,{__call=print})
> > a(10,20,30)
> 1 10 20 30
>