Comments on: The Curiously Recurring Template Pattern (CRTP)

By: Vladislav Kaplan

Vladislav Kaplan — Tue, 23 May 2017 07:05:00 +0000

Thank you

By: Jonathan Boccara

Jonathan Boccara — Sun, 21 May 2017 09:58:00 +0000

In reply to Martin Moene. Cheers, done.

By: Martin Moene

Martin Moene — Sat, 20 May 2017 14:24:00 +0000

s/itslef/itself/

By: Marek Kurdej

Marek Kurdej — Mon, 15 May 2017 07:31:00 +0000

I was thinking about the last problem you mentioned: method hiding. It’s maybe not the best solution, but you could have declared `doSomething()` in Base class as final (which implies virtual as well). Then, if you happen to override a function in a derived class, you’ll get a message like “error: overriding final function ‘void Base::doSomething() [with T = Derived]'”. Hopefully, the compiler will not add any overhead beacause of the virtual function, as it is final and not really virtual in practice.

By: Jonathan Boccara

Jonathan Boccara — Sun, 14 May 2017 00:27:00 +0000

In reply to Theldoria. Yep good point, and adding the class keyword doesn't even fix it since template classes could not be befriended.

By: James Coplien

James Coplien — Fri, 12 May 2017 18:30:00 +0000

See the original C++ Report article at: https://3aec1b23-a-eadc3f87-s-sites.googlegroups.com/a/gertrudandcope.com/info/Publications/InheritedTemplate.pdf

By: Theldoria

Theldoria — Fri, 12 May 2017 12:55:00 +0000

In reply to Jonathan Boccara.

Note that this trick does not wok in C++03:

error: in C++03 a class-key must be used when declaring a friend [-Werror=pedantic]
friend T;

By: Jonathan Boccara

Jonathan Boccara — Fri, 12 May 2017 12:27:00 +0000

In reply to Marek Kurdej.

Very cool. The reason why I didn’t mention this technique is that… I didn’t know it! 🙂 Thanks a lot for sharing Marek. I’ll include this in the post right away!

By: Marek Kurdej

Marek Kurdej — Fri, 12 May 2017 09:05:00 +0000

Hi Jonathan,
While talking about the possible error of writing `class Derived2 : public Base`, you might have talked about the solution for this problem. Namely, you can declare the base class as:

“`
template
class Base {
friend T;
Base() {}
};
“`

Base’s constructor is private, but derived class is a friend so e.g. in `Base` will allow only `Derived1` (but not `Derived2`) to access its constructor. Otherwise (if you commit the error mentioned above), you’d get an error similar to `error: use of deleted function ‘Derived2::Derived2()’.

By: Jonathan Boccara

Jonathan Boccara — Fri, 12 May 2017 08:37:00 +0000

In reply to Paul Cook. Thanks Paul, tune in on Tuesday morning then!