c++ - Forwarding template parameters -

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i trying forward template parameter parent class (from subclass), getting following error when trying so;

test.cc:9:46: error: type/value mismatch @ argument 1 in template parameter list ‘template<class a, class b> class baseclass’  class subclass : public baseclass<subclass, b> {                                               ^ test.cc:9:46: error:   expected type, got ‘subclass’

here code trying run;

#include <cstdlib>  template<typename a, typename b> class baseclass {  };  template<typename b> class subclass : public baseclass<subclass, b> { // trying forward b second parameter  };  int main(void) {     return exit_success; }

i have tried prefixing b typename, following error instead;

test.cc:9:55: error: type/value mismatch @ argument 1 in template parameter list ‘template<class a, class b> class baseclass’  class subclass : public baseclass<subclass, typename b> {                                                        ^ test.cc:9:55: error:   expected type, got ‘subclass’ test.cc:9:55: error: template argument 2 invalid 

template<typename b> class subclass : public baseclass<subclass<b>, b> //                                        ^^^ {  };

subclass injected name can used refer subclass<b> in scope of subclass. outside, name of class template (that it, requires template parameter list <> form type).

§ 9 [class]/p2:

the class-name inserted scope of class itself; known injected-class-name.

§ 3.3.2 [basic.scope.pdecl]/p8:

the point of declaration injected-class-name (clause 9) following opening brace of class definition.

§ 14.6.1 [temp.local]/p1:

like normal (non-template) classes, class templates have injected-class-name (clause 9). injected-class-name can used template-name or type-name. when used template-argument-list, template-argument template template-parameter, or final identifier in elaborated-type-specifier of friend class template declaration, refers class template itself. otherwise, equivalent template-name followed template-parameters of class template enclosed in <>.


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