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Questions tagged [crtp]

The curiously recurring template pattern (CRTP) is a C++ idiom in which a class X derives from a class template instantiation using X itself as template argument.

The curiously recurring template pattern (CRTP) is a C++ idiom in which a class X derives from a class template instantiation using X itself as template argument.

The name of this idiom was coined by Jim Coplien, who had observed it in some of the earliest C++ template code.

Typical use cases include static polymorphism and polymorphic copy construction (cloning).

Wikipedia.

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Why does CRTP not cause infinite nesting?

I am confused about how CRTP is compiled. If we have something like this: template class Base { }; class Derived : public Base { }; Why doesn't something akin to this happen during compilation? (X[Y] denotes X inherits from…
lo tolmencre
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Create alias for a list of types and passing it as a template parameter

I am using variadic templates to implement the visitor pattern: template class Visitor; template class Visitor { public: virtual void visit(Type &visitable) = 0; }; template
Nikopol
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Compiler error when using CRTP with static_assert

Consider the following code: template struct Base { static constexpr int x_base = Derived::x_derived; //static_assert(x_base > 1, "Oops"); }; struct Derived : public Base { static constexpr int x_derived = 5…
toth
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How to force use of curiously recurring template pattern in C++

I have the following base template class. template class Base { public: void do_something() { } }; It is intended to be used as a curiously recurring template pattern. It should be inherited like class B : public Base. It…
Hot.PxL
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Should members variables used by the CRTP base type be in the derived type?

I've been learning about CRTP (Curiously Recurring Template Pattern) today and believe I understand it well enough. However, in the examples I've seen the state is stored in the derived type, even though the base type relies upon their presence. To…
OMGtechy
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Compile errors for simple CRTP case with dependent types

I'm trying to use a simple form of CRTP (Curiously Recurring Template Pattern) as I've got several classes, each with several related classes, and I want a means of binding them together (eg I've got classes like Widget, Doobry and Whatsit, with…
the_mandrill
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Use of member of derived type in CRTP class

I have a curiously recurring template pattern class and a derived class like so: template class A { typedef typename Derived::C D; D x; }; class B : public A { public: class C { }; }; This fails to compile due to B not being…
Dylan
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C++ - circular dependence (using inner type of subclass in templated base class)

I run into problem with circular dependence in a templated class. There is a code sample: template struct A { typedef typename T::C D; //typename T::C c; }; struct B : public A { struct C {}; }; When I try to instantiate B,…
Loom
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CRTP + Traits class : "no type named..."

I try to implement a CRTP with templated class and I have an error with the following example code : #include template class Traits { public: typedef typename T::type type; // <- Error …
Vincent
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Can I use the Curiously Recurring Template Pattern here (C++)?

I have a C++ application that can be simplified to something like this: class AbstractWidget { public: virtual ~AbstractWidget() {} virtual void foo() {} virtual void bar() {} // (other virtual methods) }; class WidgetCollection { …
David
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C# - Intrusive tree structure, using CRTP

I'm currently working on a simple way to implement a intrusive tree structure in C#. As I'm mainly a C++ programmer, I immediatly wanted to use CRTP. Here is my code: public class TreeNode where T : TreeNode { public void AddChild(T…
s0ubap
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crtp and type visibility

I have this puzzle which I am trying to solve, and fundamentally it boils down to the following example: template struct A { typedef typename CT::VALUE_T FOO; // FOO is dependent on CT }; template struct B { typedef…
Nim
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CRTP operator= and Concepts

Clang rejects this demo, while GCC and MSVC accept it. (https://godbolt.org/z/M1Wsxs8fj) Who is correct? Or is this ill-formed no diagnosis required? #include #if 0 #define METHOD balabala // OK #else #define METHOD operator= //…
VainMan
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Three-way comparison of CRTP-ed std::vectors

In this article I've stumbled upon this obscure code (which is presented casually, like this is a totally normal C++ code): struct Tree : std::vector {}; Two trees are then created and compared (see the demo): Tree tree(size_t h) { Tree s; …
Mikhail
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Access to own private constructors via derived class constructor inheritance

Consider: struct B { void f(); private: B(int, int = 0); }; struct D : B { using B::B; }; void B::f() { auto a = D{0}; auto b = D(0); auto c = D(0, 0); D x{0}; D y(0); D z(0, 0); } GCC accepts (since 7.1; previously…
ecatmur
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