non-copyable objects and value initialization: g++ vs msvc
- by R Samuel Klatchko
I'm seeing some different behavior between g++ and msvc around value initializing non-copyable objects. Consider a class that is non-copyable:
class noncopyable_base
{
public:
noncopyable_base() {}
private:
noncopyable_base(const noncopyable_base &);
noncopyable_base &operator=(const noncopyable_base &);
};
class noncopyable : private noncopyable_base
{
public:
noncopyable() : x_(0) {}
noncopyable(int x) : x_(x) {}
private:
int x_;
};
and a template that uses value initialization so that the value will get a known value even when the type is POD:
template <class T>
void doit()
{
T t = T();
...
}
and trying to use those together:
doit<noncopyable>();
This works fine on msvc as of VC++ 9.0 but fails on every version of g++ I tested this with (including version 4.5.0) because the copy constructor is private.
Two questions:
Which behavior is standards compliant?
Any suggestion of how to work around this in gcc (and to be clear, changing that to T t; is not an acceptable solution as this breaks POD types).
P.S. I see the same problem with boost::noncopyable.
