Brian Marick
maric****@examp*****
Fri Apr 24 06:44:42 JST 2009
Suppose you have an NSArray containing some Objective-C objects. I
understand why the following can be false:
array[0] == array[0]
Each time the element is extracted from the array, it could get a new
"ruby half". The main point of this note is to confirm that's correct
behavior.
The lesser part of the note: I don't understand why the behavior isn't
consistent. Consider this program:
#! /usr/bin/env ruby
require 'osx/cocoa'
include OSX
def run(klass, count)
array = make_array(klass, count)
first = collect_the_object_ids(array)
second = collect_the_object_ids(array)
if first == second
puts "success"
else
puts "FAILURE for #{klass.name}"
puts first[0,10].inspect
puts second[0,10].inspect
end
end
def make_array(klass, count)
(0...count).collect {
klass.alloc.init
}.to_ns
end
def collect_the_object_ids(array)
array.collect { | e | e.object_id }.to_ruby
end
run(NSDictionary, 1)
run(NSString, 1)
run(NSTextField, 100000)
It consistently produces these results:
FAILURE for OSX::NSDictionary
[3079050]
[3078130]
FAILURE for OSX::NSString
[3077490]
[3077260]
success
An NSManagedObject in a 16 element NSArray had a stable object_id the
first 17 times it was extracted, then it changed.
There's caching going on in some cases. What are the rules behind
them? Thanks.
-----
Brian Marick, independent consultant
Mostly on agile methods with a testing slant
www.exampler.com, www.exampler.com/blog, www.twitter.com/marick