why we should get rid of asOop :) http://code.google.com/p/pharo/issues/detail?id=1074 Begin forwarded message:
From: "David T. Lewis" <lewis@mail.msen.com> Date: August 23, 2009 5:52:25 PM CEDT To: The general-purpose Squeak developers list <squeak-dev@lists.squeakfoundation.org
Subject: Re: [squeak-dev] Re: Newbie Question (about OOPs, maybe) (sorry) Reply-To: The general-purpose Squeak developers list <squeak-dev@lists.squeakfoundation.org
On Sun, Aug 23, 2009 at 04:36:24PM +0200, Bert Freudenberg wrote:
On 23.08.2009, at 11:42, Trygve Reenskaug wrote:
On 2009.08.22 17:26, Bert Freudenberg wrote:
On 22.08.2009, at 12:39, Trygve Reenskaug wrote:
In short: ? Smalltalk claims to be object oriented and I regard it as a serious flaw that the object ID is not explicitly visible.
What if there simply *is* no object ID? In Smalltalk, a value is a pointer to an object. Bluebook p. 564: "Each object is associated with a unique identifier called its object pointer. ..."
... digs out Blue Book ...
Yes. This is the VM implementation chapter. IMHO it does not mean an OOP has to be accessible from the image as an integer.
Smalltalk MUST have such unique identifiers to work. I see this pointer as the object's ID. I have seen from the discussion in this track that the VM can actually change this "unique" pointer.
The VM can do anything as long as you can't tell from the image. And you can't. OOPs cannot be accessed directly.
To illustrate the current behavior in Squeak, I used a plugin that displays OOP values, addresses, etc. Thus:
(1 to: 100) do: [:e | Array with: e]. "make some garbage" aString := 'Hello there'. "allocate an object" aString asOop. => 1422 "identity hash for the object" OopPlugin oopPrintStringHex: aString. '16r0FF3BE64' "current OOP value" OopPlugin machineAddressPrintStringHex: aString. '16r00002B66BBE8AE54' "C pointer to object header" Smalltalk garbageCollect. "cause objects to move around in the object memory" aString asOop. => 1422 "identity hash remains the same" OopPlugin oopPrintStringHex: aString. => '16r0FF36954' "OOP value has changed" OopPlugin machineAddressPrintStringHex: aString. => '16r00002B66BBE85944' "object has moved"
The OOP is a unique identifier for the object at a particular instant in time, but the VM is free to change it at any time without telling you.
Dave