c++ - Subclass B Inherits From a Template Class A -

c++ - Subclass B Inherits From a Template Class A<B> -

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what curiously recurring template pattern (crtp)? 3 answers

i stumbled upon code looks , can't wrap head around it:

template<typename t> class { } class b: a<b> { }

so general questions are:

why not give compile error? how can class b inherit template class a<b>, if b hasn't been defined yet? when construction ever necessary?

one of features: template pattern can help avoid vtable usage. called "static polymorphism" - http://en.m.wikipedia.org/wiki/curiously_recurring_template_pattern

suppose have code structure:

class item { public: virtual void func() = 0; } class : public item { // … } class b : public item { // … } item *item = new a(); item->func();

it can replaced this:

template<typename t> class item { public: void func() { t::func(); } } class : public item<a> { // … } class b : public item<b> { // … } item<a> *item = new a(); item->func();

this way can avoid virtual function call. can done performance improvement...

c++ templates inheritance metaprogramming