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C++ named requirements: Erasable (since C++11)

Specifies that an object of the type can be destroyed by a given Allocator.

The type T is Erasable from the container X whose value_type is identical to T if given

  • A an allocator type
  • m an lvalue of type A
  • p the pointer of type T* prepared by the container

where X::allocator_type is identical to std::allocator_traits<A>::rebind_alloc<T>,

the following expression is well-formed:

std::allocator_traits<A>::destroy(m, p);

If X is not allocator-aware or is a std::basic_string specialization, the term is defined as if A were std::allocator<T> except that no allocator object needs to be created, and user-defined specializations of std::allocator are not instantiated.

Notes​

All standard library containers require that their element type satisfies Erasable.

 
With the default allocator, this requirement is equivalent to the validity of p->~T(), which accepts class types with accessible destructors and all scalar types, but rejects array types, function types, reference types, and void.  (until C++20)  
With the default allocator, this requirement is equivalent to the validity of std::destroy_at(p), which accepts class types with accessible destructors and all scalar types, as well as arrays thereof. (since C++20)

Although it is required that customized destroy is used when destroying elements of std::basic_string until C++23, all implementations only used the default mechanism. The requirement is corrected by P1072R10 to match existing practice.

C++ named requirements: Erasable (since C++11)

Specifies that an object of the type can be destroyed by a given Allocator.

The type T is Erasable from the container X whose value_type is identical to T if given

  • A an allocator type
  • m an lvalue of type A
  • p the pointer of type T* prepared by the container

where X::allocator_type is identical to std::allocator_traits<A>::rebind_alloc<T>,

the following expression is well-formed:

std::allocator_traits<A>::destroy(m, p);

If X is not allocator-aware or is a std::basic_string specialization, the term is defined as if A were std::allocator<T> except that no allocator object needs to be created, and user-defined specializations of std::allocator are not instantiated.

Notes​

All standard library containers require that their element type satisfies Erasable.

 
With the default allocator, this requirement is equivalent to the validity of p->~T(), which accepts class types with accessible destructors and all scalar types, but rejects array types, function types, reference types, and void.  (until C++20)  
With the default allocator, this requirement is equivalent to the validity of std::destroy_at(p), which accepts class types with accessible destructors and all scalar types, as well as arrays thereof. (since C++20)

Although it is required that customized destroy is used when destroying elements of std::basic_string until C++23, all implementations only used the default mechanism. The requirement is corrected by P1072R10 to match existing practice.