The most influential thing about Self turned out to be the optimization technique called "code splitting", where you identify a "happy path" and hoist out all the expensive lookups along that path, with maybe just checks for whether you are still on it. So, for example, you emit code for one loop that just does fixed-size integers, and another one for all the other numeric types. Then at runtime, the code first checks for an int32, and then (in practice) always ends up in the fast one.
I always loved the vision of systems such as Smalltalk or Self. Interacting with software objects dynamically and having a system that is in a sense 'alive' seemed so cool to me, yet all the time later we're still sitting here typing characters into text editors to make static programs. Always wonder from time to time why interaction with programs from a developer standpoint has virtually not progressed or changed.
In some senses I think it has changed, into the modern web dev experience. You've got a living program running, handling events on the DOM, etc. And developer tools let you inspect and modify objects live, time travel in the debugger, and more. The web I think is where all the mindshare has gone for this type of programming.
The essential quality of all large, dynamically typed systems is bugginess.
Another way to say this is that if you need a reliable system made of a dynamic-type language, it has to be composed of smallish, independently testable and very thoroughly tested components. Smalltalk systems tend naturally toward the big-ball-of-mud anti-pattern. The tendency can be limited only by the self-discipline of a master craftsman in charge.
The most influential thing about Self turned out to be the optimization technique called "code splitting", where you identify a "happy path" and hoist out all the expensive lookups along that path, with maybe just checks for whether you are still on it. So, for example, you emit code for one loop that just does fixed-size integers, and another one for all the other numeric types. Then at runtime, the code first checks for an int32, and then (in practice) always ends up in the fast one.