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Re: macros

From: Helge Hess
Subject: Re: macros
Date: Fri, 23 Feb 2001 16:38:19 +0100

David Relson wrote:
> The macros have different definitions depending on the environment.  I
> don't recall all the particulars, but I remember seeing one set of
> definitions for garbage collection and another set of autorelease pools.

Exactly. GC was the initial reason to introduce the macros.

> While looking at the macros and their usage, I did notice an oddity:  In
> approx 6 modules, both AUTORELEASE and RETAIN are used.  For example in
> NSTimeZone.m, the following lines appear:
>          zone = AUTORELEASE(RETAIN(defaultTimeZone));
>          zone = AUTORELEASE(RETAIN(systemTimeZone));
> These seem really odd. 

No, this isn't odd at all. This would be odd and a NOOP:


AUTORELEASE ensures that the object will be life in the current
execution context (method/return value) / autoreleasepool transaction.

> First, using both RETAIN and AUTORELEASE gives an
> expensive NOP - their effects cancel one another (in an involved,
> time-consuming manner).  Second, with NextStep it was considered a mistake
> to call autorelease twice for the same object.  Tracing through the code, I
> found 3 occurrences of the defaultTimeZone in the autorelease pool.

You can call autorelease 100 times and it's still not a mistake, neither
on NeXTstep (with Foundation) nor on GNUstep - as long as it happens

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