9 Declarations [dcl.dcl]

9.5 Function definitions [dcl.fct.def]

9.5.3 Deleted definitions [dcl.fct.def.delete]

1
#
A function definition whose function-body is of the form = delete ; is called a deleted definition.
A function with a deleted definition is also called a deleted function.
2
#
A program that refers to a deleted function implicitly or explicitly, other than to declare it, is ill-formed.
[ Note
:
This includes calling the function implicitly or explicitly and forming a pointer or pointer-to-member to the function.
It applies even for references in expressions that are not potentially-evaluated.
If a function is overloaded, it is referenced only if the function is selected by overload resolution.
The implicit odr-use ([basic.def.odr]) of a virtual function does not, by itself, constitute a reference.
— end note
 ]
3
#
[ Example
:
One can prevent default initialization and initialization by non-doubles with 
struct onlydouble {
  onlydouble() = delete;                // OK, but redundant
  template<class T>
    onlydouble(T) = delete;
  onlydouble(double);
};
— end example
 ]
[ Example
:
One can prevent use of a class in certain new-expressions by using deleted definitions of a user-declared operator new for that class.
struct sometype {
  void* operator new(std::size_t) = delete;
  void* operator new[](std::size_t) = delete;
};
sometype* p = new sometype;     // error: deleted class operator new
sometype* q = new sometype[3];  // error: deleted class operator new[]
— end example
 ]
[ Example
:
One can make a class uncopyable, i.e., move-only, by using deleted definitions of the copy constructor and copy assignment operator, and then providing defaulted definitions of the move constructor and move assignment operator.
struct moveonly {
  moveonly() = default;
  moveonly(const moveonly&) = delete;
  moveonly(moveonly&&) = default;
  moveonly& operator=(const moveonly&) = delete;
  moveonly& operator=(moveonly&&) = default;
  ~moveonly() = default;
};
moveonly* p;
moveonly q(*p);                 // error: deleted copy constructor
— end example
 ]
4
#
A deleted function is implicitly an inline function ([dcl.inline]).
[ Note
:
The one-definition rule ([basic.def.odr]) applies to deleted definitions.
— end note
 ]
A deleted definition of a function shall be the first declaration of the function or, for an explicit specialization of a function template, the first declaration of that specialization.
An implicitly declared allocation or deallocation function ([basic.stc.dynamic]) shall not be defined as deleted.
[ Example
: 
struct sometype {
  sometype();
};
sometype::sometype() = delete;  // error: not first declaration
— end example
 ]