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pcwalton's profile
Patrick Walton
Patrick Walton
Patrick Walton
@pcwalton

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Patrick Walton

@pcwalton

Research engineer at Mozilla

San Francisco, CA
pcwalton.github.io
Joined November 2009

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    Patrick Walton‏ @pcwalton Mar 25
    • Report Tweet
    • Report NetzDG Violation

    I seriously question how committed C++ is to zero-cost abstractions when they designed and standardized an entire standard library that assumes you’re using exceptions and doesn’t really work well without them.

    8:59 PM - 25 Mar 2020
    • 11 Retweets
    • 185 Likes
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    13 replies 11 retweets 185 likes
      1. Patrick Walton‏ @pcwalton Mar 25
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        At best you can say “C++ has tried to adhere to zero-cost abstractions, but messed up when it came to exceptions, and is now stuck in a somewhat awkward place where you lose functionality if you want abstractions to be zero-cost”

        3 replies 1 retweet 42 likes
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      2. whitequark‏ @whitequark Mar 25
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        Replying to @pcwalton

        my understanding of the logic is that, in whatever cost model C++ uses, exceptions are considered zero-cost. i'm not sure if i buy that but i think i see the intent

        2 replies 0 retweets 12 likes
      3. Patrick Walton‏ @pcwalton Mar 25
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        Replying to @whitequark

        I mean, they add extra control flow edges to calls, which inhibit optimizations…

        4 replies 0 retweets 11 likes
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      2. John McCall‏ @pathofshrines Mar 26
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        Replying to @pcwalton

        This isn't really fair. The only way the STL "doesn't work well" without exceptions is that you can't trigger failures from arbitrary operations without them, but any language that allows recovery from that kind of ubiquitous failure is going to have the trade-offs of exceptions.

        2 replies 0 retweets 2 likes
      3. Patrick Walton‏ @pcwalton Mar 26
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        Replying to @pathofshrines

        I mean, what do you do if a constructor fails and you don’t have exceptions?

        2 replies 0 retweets 1 like
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      1. Patrick Walton‏ @pcwalton Mar 25
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        IMO it’s more like “C++ tried to do zero-cost abstractions, but found that adding control flow edges to every call inhibits optimizations, so they’ve tried to claw back performance in a somewhat awkward way with noexcept and -fno-exceptions”

        2 replies 3 retweets 41 likes
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      2. Arseny Kapoulkine‏ @zeuxcg Mar 26
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        Replying to @pcwalton

        You can disable exceptions and use most of the standard library just fine? Allocation failure would abort, naturally. Also, isn’t the cost of unwind/panic in Rust similar under “zero-cost” EH model?

        3 replies 0 retweets 3 likes
      3. Patrick Walton‏ @pcwalton Mar 26
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        Replying to @zeuxcg

        I’m referring to stuff like https://stackoverflow.com/questions/17337602/how-to-get-error-message-when-ifstream-open-fails … where you can’t get an error message from iostream without exceptions enabled. Rust uses Result so that you don’t need exceptions for this.

        2 replies 0 retweets 3 likes
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      2. Richard Geldreich‏ @richgel999 Mar 26
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        Replying to @pcwalton

        A dialect of C++ should exist without exceptions. I never use them. None of the numerous commercial C++ codebases I worked on over 2 decades used them.

        2 replies 1 retweet 23 likes
      3. Mike Nicolella‏ @MikeNicolella Mar 26
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        Replying to @richgel999 @pcwalton

        I agree. To the original point, I never thought of exceptions as being a “zero cost abstraction”. I usually see that term used for “this syntax crutch that does compile time checking and generates no runtime code (except for all of the nuanced rules that makes that not true)”

        1 reply 0 retweets 1 like
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