boost shared_memory_object use of deleted function - function

Question

use of deleted function in class operator=
old version worked with old compiler but not with new versions
I need this "operator=" overloading for container operation.
#include <boost/interprocess/ipc/message_queue.hpp>
#include <iostream>
using namespace boost::interprocess;
class X {
public:
size_t m_len;
shared_memory_object m_shm;
const char* m_ptr;
X():
m_len(0),
m_shm(shared_memory_object()),
m_ptr(nullptr){}
X(size_t t, const char* n):
m_len(t),
m_shm(shared_memory_object()),
m_ptr(nullptr){
shared_memory_object::remove(n);
m_shm = shared_memory_object(open_or_create,n, read_write);
m_shm.truncate (m_len);
mapped_region region(m_shm, read_write);
m_ptr = static_cast<char*>(region.get_address());
}
X(const X&& x){
m_len = x.m_len;
m_shm = x.m_shm; //error use deleted function
m_ptr = x.m_ptr;
}
virtual ~X(){}
X& operator = (const X&& a) {
if(&a == this) return *this;
m_len = a.m_len;
m_ptr = a.m_ptr;
m_shm = a.m_shm; //error use deleted function
return (*this);
}
const char* get_name(){
return m_shm.get_name();
}
};
int main ()
{
X a = X(22, "test");
X b = a; //Error
return 0;
};
The above class will be used in std::vector and operator= is needed.
boost shared_memory_object has member:
shared_memory_object(shared_memory_object &&);
shared_memory_object& operator=(shared_memory_object &&);

Answer 1

Move operations can only work on non-const objects. Why? Because it steals resources from the source instance, then it must be non-const to be modifiable. So your move operations should take non-const objects:
now should be
----------------------------------------------------------
X(const X&& x) ==> X(X&& x)
X& operator = (const X&& a) { ==> X& operator = (X&& a) {
Named variable is treated as L-value, it implies copy operations are called. You need to use std::move to cast source to R-value reference, then move operations can be called:
m_shm = std::move(x.m_shm); // in move ctor
m_shm = std::move(a.m_shm); // in move assignment operator
and finally to call move ctor:
X b = std::move(a);