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by dragonwriter
831 days ago
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> That's true, Rust has futures and those aren't objects, they're just state machines. However, "awaiting" a future causes it to execute nested inside your own, not as a new task, so it doesn't act as a traditional promise/future. That sounds like a lazy future rather than a concurrent one, but both are traditional futures. > I'm pretty sure GGP was referring to the OOP concept. Its not really an “OOP concept”. AFAICT, concurrent promises/futures or equivalent constructs mostly appeared in (often relatively obscure) functional-ish and logic languages before the mid-00s, when they started getting implemented in industrially popular, mostly OOP, languages. |
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It sort of is, because what you're doing is encapsulating the concept of "a value that may arrive in the future" with an object. Both Promises (in JS) and Futures (in Kotlin) work this way.
What I'm saying is that you don't necessarily need to encapsulate that. Rust doesn't: Futures may be called "futures", but they're actually more like "suspendable computations" (not to be confused with generators, which have their own proposal, or coroutines, which also have their own proposal). You can await one as part of another suspendable computation, but you're not holding an object that represents a concept (as in a Promise), you're holding the computation itself. By awaiting it, it becomes a part of you.
The only place a Promise/Future is necessary is when you're not using the computation directly: when you chuck a function off to a task scheduler in order for it to be executed for you. Then, in order to get anything back, you need a handle to that eventual return value. There's your Promise/Future. But if you simply don't chuck it off in the first place, and integrate it into your own suspendable computation instead, you don't need any sort of Promise/Future.
I should note that having taken a look at this library myself, it seems like both paradigms should be possible to implement on top.