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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 Feb 1
      • Report Tweet
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      Programming languages without garbage collection send us down a long path of design decisions that lead to slow compile times and fragile runtime performance cliffs.

      30 replies 41 retweets 356 likes
      Show this thread
    2. Tim Sweeney‏ @TimSweeneyEpic Feb 1
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      First is the abandoning of covariance and contravariance, the property which guarantees sensible subtyping: that bytes are also integers, and integers are also objects, extending systematically to container types and functions.

      3 replies 3 retweets 44 likes
      Show this thread
    3. Tim Sweeney‏ @TimSweeneyEpic Feb 1
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      Without garbage collection, offering an array of bytes where an array of integers is required requires stack-allocating an array of integers and converting each byte to an integer every time a subtype is used in place of an actual type. This is so absurd that it’s not done.

      6 replies 4 retweets 38 likes
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      Tim Sweeney‏ @TimSweeneyEpic Feb 1
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      So now when we want to recover performance, we need to write all containers and their operations using an increasingly elaborate set of templates or generic functions, which the compiler must specialize for each type at significant cost. This is what C++ and Rust do.

      10:18 AM - 1 Feb 2020
      • 5 Retweets
      • 40 Likes
      • Ali Shabani christophe Matthew Dixon Larry Diehl Matthieu Poullet ℭ𝔬𝔲𝔫𝔠𝔦𝔩 𝔬𝔣 ℜ𝔞𝔳𝔢𝔫𝔰 yellowknife Nick Gerace Zanin
      4 replies 5 retweets 40 likes
        1. New conversation
        2. Tim Sweeney‏ @TimSweeneyEpic Feb 1
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          Or we can create a very clunky wrapper like array_of_anything that is used wherever generic types are required, which manually casts and converts values among types dynamically each time it’s accessed. Java generics did this and they were awful.

          3 replies 4 retweets 28 likes
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        3. Tim Sweeney‏ @TimSweeneyEpic Feb 1
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          But if we have garbage collection, we can store our large data structures once with whatever type is required, then dynamically create wrappers that reinterpret it as any subtype that’s required. We pay the cost of GC and indirect control flow for accessors but that’s all.

          7 replies 4 retweets 40 likes
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        4. Tim Sweeney‏ @TimSweeneyEpic Feb 1
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          Unfortunately, most languages missed this opportunity. The C family including C# and Java are overly imperative and lost variance due to wrongly-scoped mutability. And functional languages have generally chosen type systems lacking subtypes, covariance, and contravariance.

          7 replies 5 retweets 57 likes
          Show this thread
        5. End of conversation
        1. nicebyte‏ @nice_byte Feb 1
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          Replying to @TimSweeneyEpic

          you can theoretically eschew redundant work spent on extra instantiations (which i imagine where a lion's share of the cost lies)

          0 replies 0 retweets 0 likes
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        1. L.  😷. Ritter‏ @paniq Feb 1
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          Replying to @TimSweeneyEpic

          having written a similar system, i don't think the cost _has_ to be significant. it matters what kind of cost profile you'd like to have. if you want near instant recompilation of arguably large codebases on demand, then yes, the less you do at compile time, the better.

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        1. Alexander Torstling‏ @atorstling Feb 2
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          Replying to @TimSweeneyEpic

          IMO GC in itself is fine and an elegant solution to aliasing problems like this. The problem is that almost all mainstream GC language have one giant heap, with all the problems that brings, and also that they focus too much on memory, forgetting the management of other resources

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