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yo/friends/extended.yo

 

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C++11 simplifies tt(friend) declarations by adding 

 

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    emi(extended friend) em(declarations) 

 

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    hi(friend: extended declaration)

 

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        to the language. When a class is declared as a friend, then the

 

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tt(class) keyword no longer has to be provided. E.g.,

 

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        verb(

 

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    class Friend;                   // declare a class

 

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    typedef Friend FriendType;      // and a typedef for it

 

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    using FName = Friend;           // and a using declaration

 

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    class Class1

 

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    {

 

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        friend Friend;              // FriendType and FNaem: also OK

 

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    };

 

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        )

 

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In the pre-C++11 standards the friend declaration required an explicit

 

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tt(class); e.g., tt(friend class Friend). 

 

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The explicit use of tt(class) remains required if the compiler hasn't seen

 

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the friend's name yet. E.g.,

 

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        verb(

 

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    class Class1

 

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    {

 

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        // friend Unseen;           // fails to compile: Unseen unknown.

 

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        friend class Unseen;        // OK

 

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    };

 

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        )    

 

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Section ref(TEMPFRIENDS) covers the use of extended friend declarations in

 

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class templates.

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