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No one disputes that meta programming is useful. What is disputed is C++ templates being a "good" way to meta program. I certainly understand metaprogramming,

by qppo 6y ago

No one disputes that meta programming is useful. What is disputed is C++ templates being a "good" way to meta program. I certainly understand metaprogramming, but navigating very dense C++ templates is one of the most complicated things I've had to do in my life. One or two levels of abstraction and you will lose your ability to hold everything you need to solve a problem in your head, and after a few dozen lines the source code is unreadable. > You need to understand the core language and the template language to be effective with them. this is a bug.

_se 6y ago
I guess that just hasn't been my experience at all. I don't think a nested C++ template is any more complicated than a CL macro with a corresponding level of nested `. I also don't really see how requiring understanding of a language to generate that language could be considered a bug - every macro system carries that requirement. C++ just happens to be (much) more complex than most languages (and I do agree that a large amount of that complexity is probably not necessary).
- qppo 6y ago
  I'd argue it's significantly more complex because you don't have access to the C++ AST, templates are ultimately non-hygienic macros, their results are invisible to both developer and user, and potential errors are inscrutable. They're difficult to abstract over, and you will wind up repeating yourself quite often since you can't just write normal C++ code with C++ includes for helper functions and data structures. I should be more clear about what I meant on the bug. C++ templates force you to understand the entirety of the language at once and hack around its edges because it doesn't support actual meta programming. It's hard for me to come up with a concrete example, but my experience writing some advanced compile-time evaluation with SFINAE patterns left me forgetting how things worked within minutes of typing them. Compare to say Rust, where the generics implementation is much cleaner and macro system better flushed out and easier to read/understand. Or the LISPs where your macro is just more LISP code. And not for nothing, templates destroy compile times. They take a long time to write and edit and make everyone else using them work slower. All told, templates do not make it easier to write C++ except in trivial cases and first-order abstractions.
nikki93 6y ago
The kind of stuff you are able to do with entt (https://github.com/skypjack/entt#code-example https://github.com/skypjack/entt#code-example) like `entities.view<Position, Sprite>.each([&](auto &pos, auto &vel) { ... });` is super awesome IMO. And then it compiles down to just directly inlined straight walks over the respective arrays (looking in godbolt.org). It's basically almost optimal for it. I do agree that you can go insane with templates and have a bad time. You just have to choose well. However if you have a problem with there existing other problematic code in the same language (that may be separate from your code), then C++ is maybe not the best fit. There's a lot of C++ out there.

by qppo 6y ago

_se 6y ago

I guess that just hasn't been my experience at all. I don't think a nested C++ template is any more complicated than a CL macro with a corresponding level of nested `. I also don't really see how requiring understanding of a language to generate that language could be considered a bug - every macro system carries that requirement. C++ just happens to be (much) more complex than most languages (and I do agree that a large amount of that complexity is probably not necessary).

qppo 6y ago
I'd argue it's significantly more complex because you don't have access to the C++ AST, templates are ultimately non-hygienic macros, their results are invisible to both developer and user, and potential errors are inscrutable. They're difficult to abstract over, and you will wind up repeating yourself quite often since you can't just write normal C++ code with C++ includes for helper functions and data structures. I should be more clear about what I meant on the bug. C++ templates force you to understand the entirety of the language at once and hack around its edges because it doesn't support actual meta programming. It's hard for me to come up with a concrete example, but my experience writing some advanced compile-time evaluation with SFINAE patterns left me forgetting how things worked within minutes of typing them. Compare to say Rust, where the generics implementation is much cleaner and macro system better flushed out and easier to read/understand. Or the LISPs where your macro is just more LISP code. And not for nothing, templates destroy compile times. They take a long time to write and edit and make everyone else using them work slower. All told, templates do not make it easier to write C++ except in trivial cases and first-order abstractions.

nikki93 6y ago

The kind of stuff you are able to do with entt (https://github.com/skypjack/entt#code-example https://github.com/skypjack/entt#code-example) like `entities.view<Position, Sprite>.each([&](auto &pos, auto &vel) { ... });` is super awesome IMO. And then it compiles down to just directly inlined straight walks over the respective arrays (looking in godbolt.org). It's basically almost optimal for it. I do agree that you can go insane with templates and have a bad time. You just have to choose well. However if you have a problem with there existing other problematic code in the same language (that may be separate from your code), then C++ is maybe not the best fit. There's a lot of C++ out there.