Two templates with overlap.

[Jason Heyes]

Consider these two templates:

template <class T>
std::istream &operator>>(std::istream &is, T &object);

template <class T>
std::istream &operator>>(std::istream &is, SharedPtr<T> &ptr);

What will the compiler do when it sees the following code?

Foo foo;
cin >> foo;

I presume that the compiler will instantiate the template std::istream
&operator>>(std::istream &is, T &object) with Foo. How about this code?

SharedPtr<Bar> bar;
cin >> bar;

Now I am not sure of what choice the compiler will make. Will it instantiate
the first function or the second? Thanks.

 

[Gianni Mariani]

Consider these two templates:

template <class T>
std::istream &operator>>(std::istream &is, T &object);

template <class T>
std::istream &operator>>(std::istream &is, SharedPtr<T> &ptr);

What will the compiler do when it sees the following code?

Foo foo;
cin >> foo;

I presume that the compiler will instantiate the template std::istream
&operator>>(std::istream &is, T &object) with Foo. How about this code?

SharedPtr<Bar> bar;
cin >> bar;

Now I am not sure of what choice the compiler will make. Will it instantiate
the first function or the second? Thanks.

It should instantiate the second. If you're using namespaces you may
need to have a "using namesp:perator>> blah".

 

[Chris Theis]

Consider these two templates:

template <class T>
std::istream &operator>>(std::istream &is, T &object);

template <class T>
std::istream &operator>>(std::istream &is, SharedPtr<T> &ptr);

What will the compiler do when it sees the following code?

Foo foo;
cin >> foo;

I presume that the compiler will instantiate the template std::istream
&operator>>(std::istream &is, T &object) with Foo. How about this code?

SharedPtr<Bar> bar;
cin >> bar;

Now I am not sure of what choice the compiler will make. Will it instantiate
the first function or the second? Thanks.

IMHO it should instantiate the second one. Did your compiler do it
differently?

Chris

 

[Jason Heyes]

IMHO it should instantiate the second one. Did your compiler do it
differently?

I still haven't tested it. Let me ask you. Do you think it is a good idea to
use these two templates?

template <class T>
std::istream &operator>>(std::istream &is, T &object)
{ return object.extract(is); }

template <class T>
std:stream &operator<<(std:stream &os, const T &object)
{ return object.insert(os); }

template <class T>
std::istream &operator>>(std::istream &is, SharedPtr<T> &ptr)
{
if (ptr)
{
ptr.make_unique();
return is >> *ptr;
}

T object;
if (!(is >> object))
return is;
ptr = new T(object);

return is;
}

template <class T>
std:stream &operator<<(std:stream &os, const SharedPtr<T> &ptr)
{ return os << *ptr; }


Thanks.

 

[Chris Theis]

I still haven't tested it. Let me ask you. Do you think it is a good idea to
use these two templates?

[SNIP]

Whether it's a good idea or not actually depends on your problem and the
context but from a quick glance at the code I'd say it should be okay.

Chris

 

[tom_usenet]

I still haven't tested it. Let me ask you. Do you think it is a good idea to
use these two templates?

Yes, it's fine, as long as your compiler is up to date (and therefore
supports partial ordering of function templates).

Tom

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