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Smalltalk and Self use prototyping for inheritance, like JavaScript and Lua. It's a dynamically typed version of subclassing, where your parent is itself a live

by wahern 2y ago

Smalltalk and Self use prototyping for inheritance, like JavaScript and Lua. It's a dynamically typed version of subclassing, where your parent is itself a live object, not just a definition. I suppose it's proxy-like, except forwarding of messages/method invocations is automatic and part of the language semantics, and the context object (self) is the one used in the caller's invocation. I've not used Objective C much, but I believe the core of Objective C works the same--non-overridden methods (message handlers) of an instantiated object are invoked using the parent prototype's instance definition. Objective C derives both it's semantics and technical jargon (e.g. selectors) straight from Smalltalk. But it also supports so-called protocols, aka interfaces in other languages, which because it's a more familiar paradigm seems to be how most people associate OOP with Objective C. I guess I'm making a hash of it, but in any event the end result is quite similar to if not largely indistinguishable from class inheritance. And because it's all dynamic, and depending on the language mechanics and your particular masochistic proclivities, it's even often quite straight forward to achieve multiple inheritance, e.g. in Smalltalk or Lua using a catch-all/fallback handler to select a method from a second (or third, fourth, etc) prototype subtree.

pjmlp 2y ago
Self goes one step further, in Self to create new forms of objects, first one has to clone an existing object, add the required object structure to it, dynamically, and then use it as prototype for newer instances of that form. Additionally Self, in its original form while the Java vs Self vs Smalltalk wars were going at Sun, is a full single user workstation, only with the kernel code/JIT written in C++, everything else is Self. It is this kind of plasticity that provided the brewing ground for high performance JITs, that eventually found their way into JavaScript, and why the usual "Python is too dynamic" excuse, is just that, an excuse for not wanting to spend the engineering resources that Smalltalk and Self JITs have trailed.
hayley-patton 2y ago
Smalltalk is definitely class based, though you are right for Self. It's rather unrelated to types, though I see the analogy - that said some paper on statically-typed Wyvern mentioned adopting the Self model for delegation.

by wahern 2y ago

pjmlp 2y ago

Self goes one step further, in Self to create new forms of objects, first one has to clone an existing object, add the required object structure to it, dynamically, and then use it as prototype for newer instances of that form. Additionally Self, in its original form while the Java vs Self vs Smalltalk wars were going at Sun, is a full single user workstation, only with the kernel code/JIT written in C++, everything else is Self. It is this kind of plasticity that provided the brewing ground for high performance JITs, that eventually found their way into JavaScript, and why the usual "Python is too dynamic" excuse, is just that, an excuse for not wanting to spend the engineering resources that Smalltalk and Self JITs have trailed.

hayley-patton 2y ago

Smalltalk is definitely class based, though you are right for Self. It's rather unrelated to types, though I see the analogy - that said some paper on statically-typed Wyvern mentioned adopting the Self model for delegation.