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
>
When does #t ever equal nil, outside of
a __len metamethod?
-Andrew
Well Lua could do a (probably O(n)) check to see if the table is a
sequence, and if it isn't then call __len...
