5 ms·

Are you sure you know when type-checking and when dynamic dispatching happens? Compile time is not runtime. The Java compiler is not the JVM. The compiler do

by ukj 5y ago

Are you sure you know when type-checking and when dynamic dispatching happens? Compile time is not runtime. The Java compiler is not the JVM. The compiler does type checking. The JVM does the dynamic dispatching. Neither does both.

justinpombrio 5y ago
All those statements are correct. The people downvoting you know that too. I don't think anyone has figured out what point you're trying to make, though. Could you spell it out in more detail? Consider addition. The compiler does type checking, and the JVM actually adds the numbers. Nonetheless, the addition is type checked, and does not represent a weakness of static type checking. How is dynamic dispatch different than this?
- ukj 5y ago
  The point is trivial. You can’t have both static type safety AND dynamic dispatch at the same time and in the same context about the same data. Choose one. Give up the other. Make a conscious trade off. The language that you are using is making such trade offs for you - they are implicit in the language design. Best you know what they are because they are meaningful in principle and in practice.
  - justinpombrio 5y ago
    Java has both static type safety AND dynamic dispatch at the same time and in the same context about the same data.
    - ukj 5y ago
      No, it doesn’t. The input-data to the compiler can’t be handled by the JVM and vice versa. The JVM handles byte code as input. The compiler handles source code as input. That is two different functions with two different data domains. They literally have different types! Which one of the two functions is the thing you call “Java”?
      - justinpombrio 5y ago
        A type system is sound when: for all expressions e: if e type checks with type t, then one of the following holds: - e evaluates to a value v of type t; or - e does not halt; or - e hits an "unavoidable error" like division by 0 or null deref (what counts as "unavoidable" varies from lang to lang) Notice anything interesting about this definition? It uses the word "evaluate"! Type soundness is not just a statement about the type checker. It relates type checking to run time (and thus to compilation too). That is, if you muck with Java's runtime or compiler, you can break type soundness, even if you don't change its type system in the slightest.
        ukj 5y ago
        Yes this is precisely what I am talking about. Different implementations of eval() a.k.a different programming languages have different semantics. Which implicit eval() implementation does the above hold? What type system do you have in mind such that the above holds for ALL expressions. Type-checking itself is not always decidable.
      - BoiledCabbage 5y ago
        It's pretty clear at this point you don't understand what dynamic dispatch means. I don't think it's worthwhile for anyone else to argue with you further. C++ and Java both support dynamic dispatch although you deny it. You've taken up almost a full page of HN arguing with everyone trying to explain it to you. People have pointed you to wikipedia showing you that you're wrong. [1] ISOCPP of which Bjarne is a director [2] says that C++ supports dynamic dispatch. [3] And you continue to attempt to argue that everyone on HN, Wikipedia and the creator of the C++ language are all wrong and don't know what dynamic dispatch is. Your continued insistence is both wrong and a negative impact at this point on hn. Please stop arguing something that numerous people have taken lots of patience and charity in trying every way possible to explain to you and what is clearly factually wrong. If you're going to reply, please explain why an organization that Bjarne Stroustrup is a director of believes that C++ supports dynamic dispatch. 1. https://en.wikipedia.org/wiki/Dynamic_dispatch#C++_implementation https://en.wikipedia.org/wiki/Dynamic_dispatch#C++_implement... 2 https://isocpp.org/about https://isocpp.org/about 3. https://isocpp.org/wiki/faq/big-picture#why-use-oo https://isocpp.org/wiki/faq/big-picture#why-use-oo

by ukj 5y ago

justinpombrio 5y ago

All those statements are correct. The people downvoting you know that too. I don't think anyone has figured out what point you're trying to make, though. Could you spell it out in more detail? Consider addition. The compiler does type checking, and the JVM actually adds the numbers. Nonetheless, the addition is type checked, and does not represent a weakness of static type checking. How is dynamic dispatch different than this?

ukj 5y ago
The point is trivial. You can’t have both static type safety AND dynamic dispatch at the same time and in the same context about the same data. Choose one. Give up the other. Make a conscious trade off. The language that you are using is making such trade offs for you - they are implicit in the language design. Best you know what they are because they are meaningful in principle and in practice.
- justinpombrio 5y ago
  Java has both static type safety AND dynamic dispatch at the same time and in the same context about the same data.
  - ukj 5y ago
    No, it doesn’t. The input-data to the compiler can’t be handled by the JVM and vice versa. The JVM handles byte code as input. The compiler handles source code as input. That is two different functions with two different data domains. They literally have different types! Which one of the two functions is the thing you call “Java”?
    - justinpombrio 5y ago
      A type system is sound when: for all expressions e: if e type checks with type t, then one of the following holds: - e evaluates to a value v of type t; or - e does not halt; or - e hits an "unavoidable error" like division by 0 or null deref (what counts as "unavoidable" varies from lang to lang) Notice anything interesting about this definition? It uses the word "evaluate"! Type soundness is not just a statement about the type checker. It relates type checking to run time (and thus to compilation too). That is, if you muck with Java's runtime or compiler, you can break type soundness, even if you don't change its type system in the slightest.
      - ukj 5y ago
        Yes this is precisely what I am talking about. Different implementations of eval() a.k.a different programming languages have different semantics. Which implicit eval() implementation does the above hold? What type system do you have in mind such that the above holds for ALL expressions. Type-checking itself is not always decidable.
    - BoiledCabbage 5y ago
      It's pretty clear at this point you don't understand what dynamic dispatch means. I don't think it's worthwhile for anyone else to argue with you further. C++ and Java both support dynamic dispatch although you deny it. You've taken up almost a full page of HN arguing with everyone trying to explain it to you. People have pointed you to wikipedia showing you that you're wrong. [1] ISOCPP of which Bjarne is a director [2] says that C++ supports dynamic dispatch. [3] And you continue to attempt to argue that everyone on HN, Wikipedia and the creator of the C++ language are all wrong and don't know what dynamic dispatch is. Your continued insistence is both wrong and a negative impact at this point on hn. Please stop arguing something that numerous people have taken lots of patience and charity in trying every way possible to explain to you and what is clearly factually wrong. If you're going to reply, please explain why an organization that Bjarne Stroustrup is a director of believes that C++ supports dynamic dispatch. 1. https://en.wikipedia.org/wiki/Dynamic_dispatch#C++_implementation https://en.wikipedia.org/wiki/Dynamic_dispatch#C++_implement... 2 https://isocpp.org/about https://isocpp.org/about 3. https://isocpp.org/wiki/faq/big-picture#why-use-oo https://isocpp.org/wiki/faq/big-picture#why-use-oo