"When you use a browser to access a method, the system has to retrieve the source code for that method. Initially all the source code is found in the file we refer to as the sources file. … As you are evaluating expressions or making changes to class descriptions, your actions are logged onto an external file that we refer to as the changes file. If you change a method, the new source code is stored on the changes file, not back into the sources file. Thus the sources file is treated as shared and immutable; a private changes file must exist for each user."
1984 "Smalltalk-80 The Interactive Programming Environment" page 458
But the image isn’t just the code, or classes, it’s also the network of objects (instances). And that’s more difficult to version, or to merge branches of.
Given that the instantiation of those objects has been triggered by Smalltalk commands; those Smalltalk commands can be recorded and versioned and replayed to instantiate those objects.
It means that versioning operations, even just displaying the history, effectively have to run the full image from the beginning of the history, or take intermediate snapshots of the image. In addition, there is interaction between the source code changes and the recorded command history. It also doesn't address how merging would be practical. You would have to compare the state of two images side-by-side, or rather three, for three-way merges.
"Within each project, a set of changes you make to class descriptions is maintained. … Using a browser view of this set of changes, you can find out what you have been doing. Also, you can use the set of changes to create an external file containing descriptions of the modifications you have made to the system so that you can share your work with other users."
1984 "Smalltalk-80 The Interactive Programming Environment" page 46
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The image is throw-away. It's a cache, not an archive.
"At the outset of a project involving two or more programmers: Do assign a member of the team to be the version manager. … The responsibilities of the version manager consist of collecting and cataloging code files submitted by all members of the team, periodically building a new system image incorporating all submitted code files, and releasing the image for use by the team. The version manager stores the current release and all code files for that release in a central place, allowing team members read access, and disallowing write access for anyone except the version manager."
1984 "Smalltalk-80 The Interactive Programming Environment" page 500
