I am relatively new to C++11, though I have used previous versions for many years. Is this the correct way to enforce that an object will only be movable?
class CResource
{
public:
CResource();
CResource(CResource &&);
CResource & operator=(CResource &&);
private:
CResource(const CResource &) = delete;
CResource & operator=(const CResource &) = delete;
void * m_pResource;
};
class CAcquireResource
{
public:
CResource && AcquireResource();
};
CResource && CAcquireResource::AcquireResource()
{
CResource res;
return std::move(res);
}
Edited after comments from Sebastian Redl and underscore_d
class CResource
{
public:
CResource();
CResource(CResource &&);
CResource & operator=(CResource &&);
};
class CAcquireResource
{
public:
CResource AcquireResource();
};
CResource CAcquireResource::AcquireResource()
{
CResource res;
return std::move(res);
}
Assertions are holding up aswell...
#include <type_traits>
#define STR_NAME(s) #s
#define STATIC_ASSERT_NOCOPYASSIGN(clazz) \
static_assert(!std::is_copy_assignable<clazz>::value, \
STR_NAME(clazz) " is_copy_assignable");
#define STATIC_ASSERT_NOCOPYCONSTRUCT(clazz) \
static_assert(!std::is_copy_constructible<clazz>::value, \
STR_NAME(clazz) " is_copy_constructible");
#define STATIC_ASSERT_MOVEASSIGN(clazz) \
static_assert(std::is_move_assignable<clazz>::value, \
STR_NAME(clazz) " !is_move_assignable");
#define STATIC_ASSERT_MOVECONSTRUCT(clazz) \
static_assert(std::is_move_constructible<clazz>::value, \
STR_NAME(clazz) " !is_move_constructible");
#define STATIC_ASSERT_REFERENCECLASS(clazz) \
STATIC_ASSERT_MOVEASSIGN(clazz) \
STATIC_ASSERT_MOVECONSTRUCT(clazz) \
STATIC_ASSERT_NOCOPYASSIGN(clazz) \
STATIC_ASSERT_NOCOPYCONSTRUCT(clazz)
STATIC_ASSERT_REFERENCECLASS(CResource);
These pass with Visual Studio 2017.
Your method enforces move-only.
However, the mere existence of a move constructor/assignment operator already suppresses the generation of copy constructor and assignment operator; no explicit deletion is necessary. Only a few compilers in the early days of C++11 drafts didn't correctly implement this part.
However, note that your AcquireResource
code returns a reference to a local variable and thus has undefined behavior. You should return by value.