type requirements for std::vector

Question

I am still confused about the requirements for a type to be used with a std::vector in C++11, but this may be caused by a buggy compiler (gcc 4.7.0). This code:

Answer 1

The C++11 standard does indeed require CopyInsertable as others have pointed out. However this is a bug in the C++11 standard. This has since been corrected in N3376 to MoveInsertable and DefaultInsertable.

The vector::resize(n) member function requires MoveInsertable and DefaultInsertable. These roughly translate to DefaultConstructible and MoveConstructible when the allocator A uses the default construct definitions.

The following program compiles using clang/libc++:

#include 
#include 

struct A {
  A() : X(0) { std::cerr<<" A::A(); this="< a;
  a.resize(4);
}

and for me prints out:

 A::A(); this=0x7fcd634000e0
 A::A(); this=0x7fcd634000e4
 A::A(); this=0x7fcd634000e8
 A::A(); this=0x7fcd634000ec

If you remove the move constructor above and replace it with a deleted copy constructor, A is no longer MoveInsertable/MoveConstructible as move construction then attempts to use the deleted copy constructor, as correctly demonstrated in the OP's question.