On Nov 20, 2006, at 23:13 , goran@xxxxxxxxx wrote:
Yes, the image is like a "snapshot" of RAM with live objects in it. So
an image is not the same thing as for example a jar-file in the Java
world which is just a bunch of class definitions - not objects.
That's a thing you have to deeply understand. In all object-oriented
systems that are *not* image-based (which is the huge majority), you
always start at the Big Bang - every time you run the program, it
defines classes and creates instances until it can finally start
servicing the user. Not so in Smalltalk - we make a snapshot of all
the object instances that are already fully initialized and save it
to disk. Running that image again just resumes execution wherever it
was frozen.
Indeed, the last time objects were created "from scratch" in Squeak
was like 30 years ago! From then, it's a continuous creation and
destruction of objects inside the system, snapshotted to disk from
time to time and passed to other people.
The objects in the image are the essence of Squeak, source code is
just a temporary artifact. You cannot recreate a Squeak image from
source-code alone, because in source-code only a few selected kinds
of objects are preserved. Source-code pretty much is just a textual
serialization of all instances of ClassDescription and its subclasses.
- Bert -
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