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TimSweeneyEpic's profile
Tim Sweeney
Tim Sweeney
Tim Sweeney
@TimSweeneyEpic

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Tim Sweeney

@TimSweeneyEpic

Epic Games founder & CEO

epicgames.com
Joined August 2013

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    1. Tim Sweeney‏ @TimSweeneyEpic 2 Feb 2019
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      Reactive programming is powerful, but often overlooked due to obscure syntax. Given int x,y,z; we can write z=x+y for immediate assignment. What if we could also write z~=x+y to ensure z is recalculated formulaically whenever x or y change, plus when(z) {..} to monitor changes?

      53 replies 33 retweets 334 likes
    2. Per Vognsen‏ @pervognsen 2 Feb 2019
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      Replying to @TimSweeneyEpic

      Probably fine in a language that handles value changes over time rigorously rather than as arbitrary side effects but it seems like a death trap for imperative programming; it'd still be useful in that setting too, but you'd want it to stand out and be applied very carefully.

      1 reply 0 retweets 4 likes
    3. Per Vognsen‏ @pervognsen 2 Feb 2019
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      Replying to @pervognsen @TimSweeneyEpic

      I think one thing we've learned over the past few decades is that even single-threaded event-driven/callback-driven/asynchronous programming is almost as hard to reason about as general concurrency problems and should be avoided whenever possible.

      3 replies 0 retweets 10 likes
    4. Tim Sweeney‏ @TimSweeneyEpic 2 Feb 2019
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      Replying to @pervognsen

      Perhaps this only looks like data-race-prone callbacks because of loose legacy practices. What if we were writing straightforward constraint equations, such as between a table’s overall widths, column widths, and column width percentages, and the system magically synced them?

      2 replies 0 retweets 5 likes
    5. Per Vognsen‏ @pervognsen 2 Feb 2019
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      Replying to @TimSweeneyEpic

      I think auto-updated value expressions/dataflow programming is a great idea. The tension is at the boundaries between the dataflow world and the anything-goes imperative world (your 'when' statement for value-change event handlers).

      1 reply 0 retweets 4 likes
    6. Per Vognsen‏ @pervognsen 2 Feb 2019
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      Replying to @pervognsen @TimSweeneyEpic

      Actually, not just 'when' statements but anything that can occur in a dataflow value expression that isn't "reactively referentially transparent" i.e. depends on or affects things outside the otherwise simple dataflow world.

      2 replies 0 retweets 1 like
    7. Per Vognsen‏ @pervognsen 2 Feb 2019
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      Replying to @pervognsen @TimSweeneyEpic

      Incidentally, one example of something along these lines that helps tame the practical issues (without removing them entirely) is forcing all of dataflow evaluation/recomputation to occur at a relatively quiescent program point such as the top-level game loop/run loop.

      1 reply 0 retweets 1 like
    8. Per Vognsen‏ @pervognsen 2 Feb 2019
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      Replying to @pervognsen @TimSweeneyEpic

      So each frame becomes a synchronous checkpoint for any dataflow state invariants and it lets you have dataflow value expressions depend on imperative non-dataflow state without complete chaos.

      1 reply 0 retweets 0 likes
    9. Per Vognsen‏ @pervognsen 2 Feb 2019
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      Replying to @pervognsen @TimSweeneyEpic

      It creates up to one frame of lag between the dataflow and non-dataflow world but I think it's worth it for sanity it imposes.

      2 replies 0 retweets 3 likes
      Tim Sweeney‏ @TimSweeneyEpic 2 Feb 2019
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      Replying to @pervognsen

      Interesting. The other extreme is that relational (reevaluable) assignments must be pure, and their work is done lazyily but upon any access after dependencies have changed. So you can never observe an inconsistency in relations.

      8:47 PM - 2 Feb 2019
      • 2 Likes
      • Riley Labrecque Rob "Xemu" Fermier
      1 reply 0 retweets 2 likes
        1. New conversation
        2. L.  😷. Ritter‏ @paniq 3 Feb 2019
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          Replying to @TimSweeneyEpic @pervognsen

          the feature could be done relatively safely when the dependencies are limited to function scope, but it would be helpful to see use cases that would benefit from this ... and, in the end i don't see the big difference between z~=x+y and an invalidable memoized closure z()=x+y

          1 reply 0 retweets 1 like
        3. L.  😷. Ritter‏ @paniq 3 Feb 2019
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          Replying to @paniq @TimSweeneyEpic @pervognsen

          if limited to function scope, it could be supported as a compile time solution that produces no overhead.

          0 replies 0 retweets 1 like
        4. End of conversation

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