9 Declarations [dcl]

9.6 Function definitions [dcl.fct.def]

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

1
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A deleted definition of a function is a function definition whose function-body is a deleted-function-body or an explicitly-defaulted definition of the function where the function is defined as deleted.
A deleted function is a function with a deleted definition or a function that is implicitly defined as deleted.
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A construct that designates a deleted function implicitly or explicitly, other than to declare it or to appear as the operand of a reflect-expression ([expr.reflect]), is ill-formed.
Recommended practice: The resulting diagnostic message should include the text of the unevaluated-string, if one is supplied.
[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.
For an overload set, only the function selected by overload resolution is referenced.
The implicit odr-use ([basic.def.odr]) of a virtual function does not, by itself, constitute a reference.
The unevaluated-string, if present, can be used to explain the rationale for deletion and/or to suggest an alternative.
— 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]