Class.allocate callback

ruby-talk
1

Hi.

I want to get a callback whenever an object is created in the vm. To do
this I have overridden ‘Class.new’, and it works as long as objects are
created through Object.new. But - I also want to get callbacks when
objects are created during unmarshalling of serialized data… I thought
that I could override Class.allocate to get a callback when this happens

  • but I never get the callback.

Is this a bug?

I’ve attached a simple script that illustrates my problem. Run the
script as “ruby load.rb xxx” two times in a row to see the issue.

···

load.rb

class Class
alias_method :old_new, :new
alias_method :old_allocate, :allocate

def new(*args)
    instance = old_new(*args)
    puts "Created instance #{instance}"
    return instance
end

def allocate
    instance = old_allocate
    puts "Allocated instance #{instance}"
    return instance
end

end

class Dummy
attr_reader :id, :name, :tstamp
attr_writer :name

def initialize(id, name=nil)
    @id = id
    @name = name
    @tstamp = Time.now
end

def touch
    @tstamp = Time.now
end

end

d = nil

if ARGV[0]
if File.exist?(“load.ser”)
puts "…loading from serialized file…"
File.open(“load.ser”){|f|
d = Marshal.load(f)
}
end
end

unless d
puts "…creating new instance…"
d = Dummy.new(44, “Hello”)
end

puts d.inspect
d.touch
d.name = "xxxxx"
puts d.inspect

if ARGV[0]
puts "…saving to serialized file…"
File.open(“load.ser”, “w+”){|f|
Marshal.dump(d, f)
}
end

–
/**

  • Anders Engström, aengstrom@gnejs.net
  • Your mind is like an umbrella.
  • It doesn’t work unless you open it.
  • /Frank Zappa
    */
2

Hi.

I want to get a callback whenever an object is created in the vm. To do
this I have overridden ‘Class.new’, and it works as long as objects are
created through Object.new. But - I also want to get callbacks when
objects are created during unmarshalling of serialized data… I thought
that I could override Class.allocate to get a callback when this happens

  • but I never get the callback.

Is this a bug?

[snip script]

2 fast 2 furious… I forgot one crucial piece of information:

ruby 1.8.1 (2004-02-03) [i386-linux]

//Anders

3

Hi,

···

In message “Class.allocate callback” on 04/03/19, Anders Engström aengstrom@gnejs.net writes:

I want to get a callback whenever an object is created in the vm. To do
this I have overridden ‘Class.new’, and it works as long as objects are
created through Object.new. But - I also want to get callbacks when
objects are created during unmarshalling of serialized data… I thought
that I could override Class.allocate to get a callback when this happens

  • but I never get the callback.

Is this a bug?

Not really a bug. Hooking every instance allocation might too slow
for the current implementation. Sometimes I have to choose
performance over flexibility.

Marshal.load takes optional second argument, which is a proc called
for each unmarshalled object.

						matz.
4

Hi,

I want to get a callback whenever an object is created in the vm. To do
this I have overridden ‘Class.new’, and it works as long as objects are
created through Object.new. But - I also want to get callbacks when
objects are created during unmarshalling of serialized data… I thought
that I could override Class.allocate to get a callback when this happens

  • but I never get the callback.

Is this a bug?

Not really a bug. Hooking every instance allocation might too slow
for the current implementation. Sometimes I have to choose
performance over flexibility.

Thanks for the reply. I can understand this decision - it makes sense.
It would be nice if this behaviour was documented though :slight_smile:

Coming from the Java world I would say that Ruby is flexible enough,
even without callback-on-allocate. And - coming from the Java world it’s
absolutely wonderful to ask a question in a ng and get a reply from the
actual author of the language in < 24 hours :slight_smile:

(I wonder if James Gosling frequents comp.lang.java… :wink:

//Anders

···

In message “Class.allocate callback” > on 04/03/19, Anders Engström aengstrom@gnejs.net writes:

–
/**

  • Anders Engström, aengstrom@gnejs.net
  • Your mind is like an umbrella.
  • It doesn’t work unless you open it.
  • /Frank Zappa
    */