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- Subject: Re: Standard Libraries:
- From: Javier Guerra <javier@...>
- Date: Thu, 31 Dec 2009 07:31:11 -0500
steve donovan wrote:
> Would be interesting to know the actual cost of allowing strings to
> have individual metatables.
local a = setmetatable ("some string", metatable1)
local b = setmetatable ("some ", metatable2)
local c = setmetatable ("string", metatable2)
local d = b..c
if you forget about metatables, you'll find that a and d both are the _same_ string, and comparing them for equality is only a pointer comparison. that's possible because of string immutability.
but if each string can have a different metatable... are a and d still the _same_ string? what metatable should it have?
local a = "anything"
local b = a
a = setmetatable (a, yourmetatable)
is b==a ? what's the metatable of b?
if now a is a different value and b~=a, is a=="anything" still?
so, i think that immutable values have to share a single metatable for the whole type.