CODEWITHSUNDEEP
c++constructorstd-pair
Bojack
Bojack

Reputation: 479

Can not Create pair - constructor

I can not create a pair when one of the classes in the pair in a class Edge I know it is because of the constructors in Edge, but I do not know what is wrong.

The Edge constructor has a Token because I wanted to make sure that only an Object of type Vertex can create an object Edge.

class Edge
{
public:
   class ConstructionToken
   {
   private:
      ConstructionToken();
      friend class Vertex;
   };

   Edge( const Edge &) = default;
   Edge( const ConstructionToken & ){};

private
   //weight, etc...
};

void
Vertex::insert_edge( const std::string & end_point )
{
   Edge new_edge( Edge::ConstructionToken );
   std::pair<std::string,Edge> temp( end_point, new_edge );
   //edges.insert( temp );


}

Compiling error

lib/Vertex.cpp:12:32: error: no matching constructor for initialization of 'std::pair<std::string, Edge>'
   std::pair<std::string,Edge> temp( end_point, new_edge );
                               ^     ~~~~~~~~~~~~~~~~~~~
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/utility:262:5: note: candidate constructor not viable: no known conversion
      from 'Edge (Edge::ConstructionToken)' to 'const Edge' for 2nd argument
    pair(const _T1& __x, const _T2& __y)

Upvotes: 0

Views: 3134

Answers (1)

Mike Seymour
Mike Seymour

Reputation: 254431

This

Edge new_edge( Edge::ConstructionToken );

declares a function, since the name in parentheses is a type. To declare a variable, use

Edge new_edge{ Edge::ConstructionToken{} };  // C++11 or later
Edge new_edge((Edge::ConstructionToken())); // Historic dialects

Upvotes: 4

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