Some weeks ago, I added environments to my open source AjTalk Smalltalk Virtual Machine, C# version. What is an environment, in my jargon? It’s a dictionary for named artifacts, like classes. Smalltalk global is a classical environment. But I want to add support of other named environments, to avoid class name collisions. Usually, classic Smalltalk have pool dictionaries, but I want something more dynamic. Then, I added Environment, see my tests:
At first, Smalltalk is the current environment:
"Current environment is Smalltalk" [Environment current == Smalltalk] assert.
You can create new environments:
env := Environment new: #MyEnvironment.
Automatically, the new environment is registered/added to the current one, in this case, Smalltalk:
"The new environment was defined as global at Smalltalk" [(Smalltalk at: #MyEnvironment) isNil not] assert. [(Smalltalk at: #MyEnvironment) == MyEnvironment] assert. [(Smalltalk at: #MyEnvironment) == env] assert. [MyEnvironment isNil not] assert. [MyEnvironment == env] assert.
Every new Environment has an entry to Smalltalk:
"Dotted expression syntax sugar for MyEnvironment at: #Smalltalk" [MyEnvironment.Smalltalk == Smalltalk] assert.
You can switch to a new environment:
env setCurrent. "Current environment check" [Environment current == env] assert. [Environment current == Smalltalk.MyEnvironment] assert.
And then, this is the key feature, the class definitions define a new class AT CURRENT environment:
"Define a class at current env environment, no change to syntax" Object subclass:#MyClass instanceVariableNames:'' classVariableNames:'' poolDictionaries:'' category:'' . [(env at: #MyClass) isNil not] assert. [(Smalltalk at: #MyClass) isNil] assert.
Orthogonally to environments, I implemented modules: a way to search and load file outs, and running them at a new environment (similar to Python import, or (more or less) to Node.js/CommonJS require). But this is a topic for another post 😉
Angel “Java” Lopez