C++ named requirements: ImplicitLifetimeType

Note: the standard doesn't define a named requirement with this name. This is a type category defined by the core language. It is included here as a named requirement only for consistency.

Requirements

The following types are collectively called implicit-lifetime types:

• scalar types
• implicit-lifetime class types
• arrays of such types
• cv-qualified versions of these types

Notes

Certain operations may implicitly create and start the lifetime of objects of implicit-lifetime types, if doing so would prevent undefined behavior. However, such operations do not start the lifetimes of subobjects of such objects that are not themselves of implicit-lifetime types.

The following operations may implicitly create objects:

• An operation that begins the lifetime of an array of unsigned char or std::byte (od C++17).

• An invocation of std::aligned_alloc (od C++17), std::calloc, std::malloc, or std::realloc.

• Any implicit or explicit invocation of a function named operator new or operator new[] (including non-allocating and user-defined placement allocation functions). Including

  • std::allocator::allocate
  • std::allocator::allocate_at_least (od C++23)
• An invocation of std::memory_resource::allocate, regardless of how storage is obtained. Including  (od C++17)
  • std::pmr::polymorphic_allocator::allocate
  • std::pmr::polymorphic_allocator::allocate_bytes (od C++20)
  • std::pmr::polymorphic_allocator::allocate_objects (od C++20)

• An invocation of std::memcpy or std::memmove.

• An invocation of std::bit_cast (od C++20)
• An invocation of std::start_lifetime_as or std::start_lifetime_as_array. (od C++23)

• An assignment expression that involves union members if the union's assignment operator is built-in or trivial.

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
CWG 2489	C++20	an operation that begins the lifetime of a char array implicitly creates objects	it does not