9 Declarations [dcl.dcl]

9.5 Function definitions [dcl.fct.def]

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

1
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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.
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A program that refers to a deleted function implicitly or explicitly, other than to declare it, is ill-formed.
[Note 1:
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]
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[Example 1:
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 2:
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 3:
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]
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A deleted function is implicitly an inline function ([dcl.inline]).
[Note 2:
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 4: struct sometype { sometype(); }; sometype::sometype() = delete; // error: not first declaration — end example]