Re: [ANN] Lua 5.2.0 (work2) now available

[Ignacio Burgueño <ignaciob@...>]

On 14/01/2010 19:14, Luiz Henrique de Figueiredo wrote:
> > __len is still able to return non number values. What is the position
> > about that? Is that the desired behaviour?
>
> __len can return any Lua value:
>
> for k,v in ipairs({true,print,"hello",{},io.stdin}) do
> 	a=setmetatable({},{__len=function() return v end})
> 	print(k,v,#a)
> end
>
> 1	true	true
> 2	function: 0x9bbdfd0	function: 0x9bbdfd0
> 3	hello	hello
> 4	table: 0x9bc2240	table: 0x9bc2240
> 5	file (0x2e5420)	file (0x2e5420)


Well, as Mike pointed out, __add can return non number values and that 
is reasonable. For instance, a vector library so that v3 = v1 + v2 will 
benefit from __add being able to return anything.
But I can't think of a case where the length of something is not a 
numeric value.

For me, __len has clear semantics. The length of something is measurable 
in 'n' units, with 'n' being a number.

Using __len for other uses seems like a case of operator overloading 
abuse (C++).

Even the common idiom of "t[#t + 1] = something" will have to take care 
of checking the type of #t before doing arithmetic with it.

And in a related note, if now there is lua_rawlen, shouldn't it have a 
non-raw version, like gettable / rawget, etc?

Regards,
Ignacio