On 31.12.2013, at 08:53, David Holiday <neubu...@rohan.sdsu.edu> wrote:
> Is there a way to browse the ecosystem of objects in a Smalltalk image?
Yes, multiple ones in fact. This is a major reason working in Smalltalk feels
more immediate than in other environments.
> I'm not talking about the class browser, what I'm looking for is a way to see
> what objects have actually been instantiated and what their state is.
The basic tool for this is called an Inspector. Whenever you have an
expression, like "3 + 4", you press cmd-i to "inspect it", which opens an
inspector on the result. This works in any text area. Try for example
inspecting "self" in a class browser, and you will inspect the underlying class
object (which the browser shows a high-level view of).
In the Inspector you see the objects referenced by this object (via instance
variables or indexed fields) in the left panel. Select any of them and choose
"inspect" from the context menu (or press cmd-i again). This way you can
inspect all the objects in the system.
A more modern tool than the Inspector (which was around 40 years ago already)
is the Object Explorer. It presents you a tree view of an object and its
"children", which again are the instance variables and indexed fields of the
object. Open it with cmd-shift-i (or "explore" in the context menu).
You can also do the reverse. If you choose "objects pointing to this value" you
get an inspector showing all the objects that directly point to this object.
Similarly there is a "reverse explorer", which you can open by selecting
"explore pointers".
There are two roots to all the objects in the system:
Smalltalk specialObjectsArray
which basically holds everything the Virtual Machine needs to know about, and
in turn almost every object in the whole image, and
thisContext
which is the current execution context, holding onto temporary objects. When a
garbage collection is performed, any object not reachable form either of these
two roots is removed from memory.
An "interesting" global object to explore is
Project current
which holds your current workspace, in particular
Project current world
, the root of all morphs in the world. And of course
Smalltalk
itself is the dictionary that holds all global objects, including all classes
(unless they are defined in a non-global environment).
There is also a low-level way to enumerate all objects in memory. "self
someObject" will return the very first object in memory (which happens to be
the nil object), and "anObject nextObject" will return the next one:
| object count |
count := 0.
object := self someObject.
[0 == object]
whileFalse: [count := count + 1.
object := object nextObject].
count
Interestingly, this also finds objects that are due to be garbage-collected.
For example, if you accidentally closed a text window, there is a good chance
its contents will still be in memory, and can be retrieved using an expression
like
ByteString allInstances last: 10
This makes use of the someInstance/nextInstance methods, which are similar to
someObject/nextObject, but restricted to instances of one class only.
Hope you have fun poking around in the world of objects :)
- Bert -
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