On 14/01/2010 19:14, Luiz Henrique de Figueiredo wrote:
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?__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)
Regards, Ignacio