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> But there's a reason the crowd is moving against inheritance. I doubt it; the majority of code is in enterprise projects, and they do Java and C# in the idio

> But there's a reason the crowd is moving against inheritance. I doubt it; the majority of code is in enterprise projects, and they do Java and C# in the idiomatic way, with inheritance. I'm working on an Android project right now, and inheritance is everywhere! So, sure, if you ignore all mobile development, and ignore almost all enterprise software, and almost all internal line-of-business software, and restrict yourself to what various "influencers" say, then sure THAT crowd is moving away from inheritance.

lmm 2y ago
Java and C# are already a huge step up from what came before, since they at least introduce the concept of an interface as a distinct thing from a parent class. The fact that you don't notice that is proof that progress does happen, if only slowly.
- pasc1878 2y ago
  Java wasn't the first to do that Objective-C (10? years before) had interfaces. Even C++ has that with multiple inheritance - some parents can just be interfaces. As to whether Smalltalk needs interfaces see https://stackoverflow.com/a/7979852/151019 https://stackoverflow.com/a/7979852/151019 and https://www.jot.fm/issues/issue_2002_05/article1/ https://www.jot.fm/issues/issue_2002_05/article1/
  - lmm 2y ago
    Objective-C and Smalltalk were always niche languages, at least by comparison to Java and C#, and I think Smalltalk fans underestimate the value of many things. C++ does not (or at least did not at the time) have a concept of interfaces. There was a pattern in some development communities for defining interfaces by writing classes that followed particular rules, but no first-class support for them in the language.
    - kgeist 2y ago
      >no first-class support for them in the language. An interface is just a base class none of whose virtual functions have implementations. C++ has first class support for it. The only thing C++ lacks is the "interface" keyword.
      - gpderetta 2y ago
        The main reason (other than self-documentation) that some other languages separate interfaces form normal classes is that they only support multiple inheritance for interfaces. C++ doesn't have this restriction, so interfaces would add very little.
        colejohnson66 2y ago
        Because multiple inheritance causes the diamond problem. C# forces you to solve it by declaring one method as the "canonical" and the others as "explicit interface implementations" (only accessible if the variable/receiver is typed as that interface).
        layer8 2y ago
        The diamond problem strictly speaking only has to be one when the common base class has constructor arguments. While a Java-style interface construct makes it easy to prevent, it also imposes much stronger restrictions than the above. It would have been possible to only impose the above restriction. Yes, there are failure cases with separate compilation, but the way Java dynamically loads classes, that would be similar to how when the JVM loads a class file that is supposed to be an interface, it discovers that instead it has been changed to a class.
    - lelanthran 2y ago
      > C++ does not (or at least did not at the time) have a concept of interfaces. There was a pattern in some development communities for defining interfaces by writing classes that followed particular rules, but no first-class support for them in the language. Your distinction between "first class support for interfaces" and "C++ support for interfaces" looks like an artificial one to me. Other than not requiring the keyword "interface", what is it about the C++ way of creating an interface that makes it not "first class support"?
  - igouy 2y ago
    Also: 2003 Traits: Composable Units of Behaviour https://www.cs.cmu.edu/~aldrich/courses/819/Scha03aTraits.pdf https://www.cs.cmu.edu/~aldrich/courses/819/Scha03aTraits.pd... " Traits as described in this paper are implemented in Squeak [22], an open-source dialect of Smalltalk-80."

lmm 2y ago

Java and C# are already a huge step up from what came before, since they at least introduce the concept of an interface as a distinct thing from a parent class. The fact that you don't notice that is proof that progress does happen, if only slowly.

pasc1878 2y ago
Java wasn't the first to do that Objective-C (10? years before) had interfaces. Even C++ has that with multiple inheritance - some parents can just be interfaces. As to whether Smalltalk needs interfaces see https://stackoverflow.com/a/7979852/151019 https://stackoverflow.com/a/7979852/151019 and https://www.jot.fm/issues/issue_2002_05/article1/ https://www.jot.fm/issues/issue_2002_05/article1/
- lmm 2y ago
  Objective-C and Smalltalk were always niche languages, at least by comparison to Java and C#, and I think Smalltalk fans underestimate the value of many things. C++ does not (or at least did not at the time) have a concept of interfaces. There was a pattern in some development communities for defining interfaces by writing classes that followed particular rules, but no first-class support for them in the language.
  - kgeist 2y ago
    >no first-class support for them in the language. An interface is just a base class none of whose virtual functions have implementations. C++ has first class support for it. The only thing C++ lacks is the "interface" keyword.
    - gpderetta 2y ago
      The main reason (other than self-documentation) that some other languages separate interfaces form normal classes is that they only support multiple inheritance for interfaces. C++ doesn't have this restriction, so interfaces would add very little.
      - colejohnson66 2y ago
        Because multiple inheritance causes the diamond problem. C# forces you to solve it by declaring one method as the "canonical" and the others as "explicit interface implementations" (only accessible if the variable/receiver is typed as that interface).
        layer8 2y ago
        The diamond problem strictly speaking only has to be one when the common base class has constructor arguments. While a Java-style interface construct makes it easy to prevent, it also imposes much stronger restrictions than the above. It would have been possible to only impose the above restriction. Yes, there are failure cases with separate compilation, but the way Java dynamically loads classes, that would be similar to how when the JVM loads a class file that is supposed to be an interface, it discovers that instead it has been changed to a class.
  - lelanthran 2y ago
    > C++ does not (or at least did not at the time) have a concept of interfaces. There was a pattern in some development communities for defining interfaces by writing classes that followed particular rules, but no first-class support for them in the language. Your distinction between "first class support for interfaces" and "C++ support for interfaces" looks like an artificial one to me. Other than not requiring the keyword "interface", what is it about the C++ way of creating an interface that makes it not "first class support"?
- igouy 2y ago
  Also: 2003 Traits: Composable Units of Behaviour https://www.cs.cmu.edu/~aldrich/courses/819/Scha03aTraits.pdf https://www.cs.cmu.edu/~aldrich/courses/819/Scha03aTraits.pd... " Traits as described in this paper are implemented in Squeak [22], an open-source dialect of Smalltalk-80."