4 ms·

I had a similar feeling. As a long-time C# programmer (how old is C#? That many years), I look at this and get really wide-eyed, "how is that at all a good idea

I had a similar feeling. As a long-time C# programmer (how old is C#? That many years), I look at this and get really wide-eyed, "how is that at all a good idea?!" A lot of these features seem like ways to hack around the fact that C++ templates are not generics, they are literally templates for writing copies of classes. It seems like features like this are going to make code size explode. A lot of the examples also seem very smelly from an OOP perspective. We should one class be able to have different fields depending on template parameters? That seems like something one should do in a subclass.

mattnewport 8y ago
I'm very familiar with C++ and C# and overall I find I like C++ a lot better. There are a few nice convenience features of C# but knowing both languages I tend to find whenever they differ I feel like C++ made the better design choice. And C# going all in on OOP is a part of that. It's reasonably clear now that OOP was mostly a big mistake and a dead end. C++ is less infected by going all in on it as it has always been a multi paradigm language.
adrianN 8y ago
I'm not sure what you mean by generics if you think that C++ templates are not a kind of generics. Do you prefer that everything happens at runtime? Similarly, subclasses as opposed to templates carry a runtime cost. Virtual function calls are not free. Why pay that cost if you can deduce the right code from the types at compiletime? Besides, and this is probably a matter of opinion, I find code hard to follow that uses inheritance heavily.
- Retra 8y ago
  By "generics", I presume they mean template parameters which are checked at declaration, not at use.
  - mattnewport 8y ago
    That sounds like concepts, as used extensively in the OP.
    - steveklabnik 8y ago
      One significant difference with concepts is that they are optional.
      - mattnewport 8y ago
        Gradual typing is mostly a good thing for metaprogramming I think. Even if it was just a compromise for backwards compatibility I'd still take it over C#'s rather limited generics.
        steveklabnik 8y ago
        I think C# is a good language, but I also am not sure that it's a poster child for this particular language feature. (I mean this literally; I don’t have enough experience to really know how it compares to the usual suspects in this area.)
        mattnewport 8y ago
        A bit of a test case for me, coming from the domain of games / 3D graphics programming, as to whether a language has a 'sufficiently powerful' generics feature set is whether it is possible to implement a generic 'short vector' type as used in any type of graphics programming. I think 'good' generics / metaprogramming support should let you meet most of these goals in a generic 'short vector' type: - Support 'n' dimensional vectors (2, 3 and 4 are the only ones commonly used in 3D graphics and games). - Support a choice of underlying element type (at least float, double and int but it's handy to be able to support custom types like a fixed point or rational type too). - Support operator overloading for natural expression of things like adding two vectors. - Be very close or identical in performance to the equivalent hand written variant for every combination of dimension / element type (excluding optimizations for particular SIMD element widths etc.) - Not be significantly worse for debugging than the equivalent hand written code (this is as much a tooling issue as a language issue). It's possible to meet all of these requirements in modern C++ without using any particularly exotic metaprogramming functionality. It's impossible in C#. I don't know of any other language that meets these requirements as well as C++ although I'm not really familiar with the facilities offered by e.g. Rust.
- seanmcdirmid 8y ago
  C++ supports generic through template/macro expansion, rather than through parametric polymorphism.

mattnewport 8y ago

I'm very familiar with C++ and C# and overall I find I like C++ a lot better. There are a few nice convenience features of C# but knowing both languages I tend to find whenever they differ I feel like C++ made the better design choice. And C# going all in on OOP is a part of that. It's reasonably clear now that OOP was mostly a big mistake and a dead end. C++ is less infected by going all in on it as it has always been a multi paradigm language.

adrianN 8y ago

I'm not sure what you mean by generics if you think that C++ templates are not a kind of generics. Do you prefer that everything happens at runtime? Similarly, subclasses as opposed to templates carry a runtime cost. Virtual function calls are not free. Why pay that cost if you can deduce the right code from the types at compiletime? Besides, and this is probably a matter of opinion, I find code hard to follow that uses inheritance heavily.

Retra 8y ago
By "generics", I presume they mean template parameters which are checked at declaration, not at use.
- mattnewport 8y ago
  That sounds like concepts, as used extensively in the OP.
  - steveklabnik 8y ago
    One significant difference with concepts is that they are optional.
    - mattnewport 8y ago
      Gradual typing is mostly a good thing for metaprogramming I think. Even if it was just a compromise for backwards compatibility I'd still take it over C#'s rather limited generics.
      - steveklabnik 8y ago
        I think C# is a good language, but I also am not sure that it's a poster child for this particular language feature. (I mean this literally; I don’t have enough experience to really know how it compares to the usual suspects in this area.)
        mattnewport 8y ago
        A bit of a test case for me, coming from the domain of games / 3D graphics programming, as to whether a language has a 'sufficiently powerful' generics feature set is whether it is possible to implement a generic 'short vector' type as used in any type of graphics programming. I think 'good' generics / metaprogramming support should let you meet most of these goals in a generic 'short vector' type: - Support 'n' dimensional vectors (2, 3 and 4 are the only ones commonly used in 3D graphics and games). - Support a choice of underlying element type (at least float, double and int but it's handy to be able to support custom types like a fixed point or rational type too). - Support operator overloading for natural expression of things like adding two vectors. - Be very close or identical in performance to the equivalent hand written variant for every combination of dimension / element type (excluding optimizations for particular SIMD element widths etc.) - Not be significantly worse for debugging than the equivalent hand written code (this is as much a tooling issue as a language issue). It's possible to meet all of these requirements in modern C++ without using any particularly exotic metaprogramming functionality. It's impossible in C#. I don't know of any other language that meets these requirements as well as C++ although I'm not really familiar with the facilities offered by e.g. Rust.
seanmcdirmid 8y ago
C++ supports generic through template/macro expansion, rather than through parametric polymorphism.