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Message from discussion Comparing Object Identity
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Dave Whipp  
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 More options Dec 12 2002, 5:48 pm
Newsgroups: perl.perl6.language
From: david_wh...@fast-chip.com (Dave Whipp)
Date: Thu, 12 Dec 2002 14:42:49 -0800
Local: Thurs, Dec 12 2002 5:42 pm
Subject: Re: Comparing Object Identity
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"Dan Sugalski" <d...@sidhe.org> wrote in message

news:a05200f00ba1ebb73c6d2@[63.120.19.221]...

> There'll definitely be memory address reuse. If .id returns the
> current object's memory address, it shouldn't be cached any place, as
> otherwise you'll find things going bang with some regularity.

In a multi-threaded environment, even a simple

  $a.id == $b.id

may have significant time between the two lookups. If we are
going to rely on addresses for id comparison, then we need to
mandate that the address is constant for the life of the object.
Brent indicated that he could think of no reason for the "header
address" to change: but that isn't strong enough. We need a cast-
iron guarantee. Otherwise we can't compare identity using .id.

Dave.


 
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