Friend template operator overload

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Class declaration. Access specifiers. Virtual function. Default constructor. Copy constructor. Copy assignment. Class template. When a friend declaration refers to a full specialization of a function template, the keyword inline and default arguments cannot be used:. A template friend declaration can name a member of a class template A, which can be either a member function or a member type the type must use elaborated-type-specifier.

Such declaration is only well-formed if the last component in its nested-name-specifier the name to the left of the last :: is a simple-template-id template name followed by argument list in angle brackets that names the class template.

The template parameters of such template friend declaration must be deducible from the simple-template-id. In this case, the member of any specialization of A becomes a friend. This does not involve instantiating the primary template A: the only requirements are that the deduction of the template parameters of A from that specialization succeeds, and that substitution of the deduced template arguments into the friend declaration produces a declaration that would be a valid redeclaration of the member of the specialization:.

Default template arguments are only allowed on template friend declarations if the declaration is a definition and no other declarations of this function template appear in this translation unit. A common use case for template friends is declaration of a non-member operator overload that acts on a class template, e.

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Expressions Value categories Order of evaluation. Operators Operator precedence. Class declaration Constructors this pointer. However, it is generated by the class template. Generating non-template functions from a template is a bit hazy. For example, you cannot add a declaration for that function outside the class block.

Therefore you must define it inside the class block as well, which makes sense because the class template will generate it.

You can only find it through argument-dependent meaning overload resolution, i. Sorry, contrived example. Probably, you have nothing to worry about, as long as the function in question is an operator. Or, you can change the friend to be a template as well. This is quite an old topic but I think the easiest way to declare the operator is to define it inside Float class. The syntax is easier to write and understand and it will work exactly the same except that it will be inlined , it will no be a member function.

MSDN: Friend functions defined inside class declarations are not considered in the scope of the enclosing class; they are in file scope. This declares a full specialization of the operator template a friend of a specific instance of the class template. In a comment to the question UncleBens has kindly provided a link to an explanation why that is so complicated.

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