In cppreference, function declaration, under the section User-provided functions. There is a sentence:

Declaring a function as defaulted after its first declaration can provide efficient execution and concise definition while enabling a stable binary interface to an evolving code base.

The main question is =default and =delete is a function declaration or a function definition?

Shoudn't that be

Defining a function as defaulted after its first declaration?

CodePudding user response：

In the same sense we can also argue that the term declaring as defaulted should be transformed into defining as defaulted, because when we declare a function as defaulted, it actually generates the definition of the function. So here

struct triv
{
    triv() = default;
};

We at the same time declare it's default constructor, and henceforth define it. I think it is called declaring as defaulted, because of syntax being similar more to a declaration of a function than a definition of a function. Also in C 11 standard, in 8.4.2.4. It is noted that

A user-provided explicitly-defaulted function (i.e., explicitly defaulted after its first declaration) is defined at the point where it is explicitly defaulted.

So I think it is redundant to search for a difference in terms defaulting a function, declaring as defaulted and defining as defaulted.

CodePudding user response：

Those are definitions. But like most (all?) definitions, they're also declarations.

[dcl.fct.def.delete]/1:

A deleted definition of a function is a function definition whose ...

[dcl.fct.def.default]/1:

A function definition whose function-body is of the form = default ; is called an explicitly-defaulted definition ...