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Rageking890 (talk | contribs) Add simplified CRTP with C++23 feature, deducing this |
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==History==
The technique was formalized in 1989 as "''F''-bounded quantification."<ref>{{cite web|url=http://cs.utexas.edu/~wcook/papers/FBound89/CookFBound89.pdf|title=F-Bounded Polymorphism for Object-Oriented Programming|author=William Cook|date=1989|display-authors=etal}}</ref> The name "CRTP" was independently coined by [[Jim Coplien]] in 1995,<ref>{{cite journal | author=Coplien, James O. | title=Curiously Recurring Template Patterns | journal=C++ Report | date=February 1995 | pages=24–27 | url=
The Microsoft Implementation of CRTP in [[Active Template Library]] (ATL) was independently discovered, also in 1995, by Jan Falkin, who accidentally derived a base class from a derived class. Christian Beaumont first saw
== General form ==
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// ...
};
</syntaxhighlight>{{clarify|reason=members within Base<T> can use what template and what would that look like?|date=June 2025}}
Some use cases for this pattern are [[Template metaprogramming#Static polymorphism|static polymorphism]] and other metaprogramming techniques such as those described by [[Andrei Alexandrescu]] in ''[[Modern C++ Design]]''.<ref>{{cite book | first=Andrei | last=Alexandrescu | authorlink=Andrei Alexandrescu | title=Modern C++ Design: Generic Programming and Design Patterns Applied | publisher=Addison-Wesley | isbn=0-201-70431-5 | year=2001}}</ref>
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};
struct Derived : public Base<Derived>
{
void implementation();
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</syntaxhighlight>
In the above example, the function <code>Base<Derived>::interface()</code>, though ''declared'' before the existence of the <code>struct Derived</code> is known by the compiler (i.e., before <code>Derived</code> is declared), is not actually ''instantiated'' by the compiler until it is actually ''called'' by some later code which occurs ''after'' the declaration of <code>Derived</code> (not shown in the above example), so that at the time the function "
This technique achieves a similar effect to the use of [[virtual function]]s, without the costs (and some flexibility) of [[dynamic polymorphism]]. This particular use of the CRTP has been called "simulated dynamic binding" by some.<ref>{{cite web | url=http://www.pnotepad.org/devlog/archives/000083.html | title=Simulated Dynamic Binding | date=7 May 2003 | accessdate=13 January 2012 | url-status=dead | archiveurl=https://web.archive.org/web/20120209045146/http://www.pnotepad.org/devlog/archives/000083.html | archivedate=9 February 2012 }}</ref> This pattern is used extensively in the Windows [[Active Template Library|ATL]] and [[Windows Template Library|WTL]] libraries.
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==Deducing this==
The use of CRTP can be simplified using the [[C++23]] feature
}}</ref><ref>{{Cite web|title=Explicit object parameter|url=https://en.cppreference.com/w/cpp/language/member_functions#Explicit_object_parameter|access-date=27 December 2023}}</ref> For the function <code>signature_dish</code> to call a derived member function <code>cook_signature_dish</code>, <code>ChefBase</code> needs to be a templated type and <code>CafeChef</code> needs to inherit from <code>ChefBase</code>, passing
<syntaxhighlight lang="cpp">
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