template<typename T>template<class T>Typename
Author
Hi everyone,
I've recently started learning about templates, and I have a question. I've seen templates declared as
They're equivalent. There are two reserved words that mean the same thing in this context for historical reasons; see here
Author
Thanks for the replies, that makes sense now.
One last thing. With
and
Would there be an error if T did not contain an A?
One last thing. With
T::A *aObjand
typename T::A* a6;Would there be an error if T did not contain an A?
Quote:Original post by Aiwendil
Thanks for the replies, that makes sense now.
One last thing. WithT::A *aObj
andtypename T::A* a6;
Would there be an error if T did not contain an A?
Of course.
Their example about using class instead of typename is one of the more interesting cases, and one that can cause confusion.
The first example says to take the value of A within the scope T, and multiply it by aObj. It is a subtle error, and generally not what the programmer meant. The code will work if you meant to do this:
class T {
public:
const int A = 4;
};
If A is not a value, the code should not compile.
The second says to create a pointer of T::A, which must be a type.
class T {
public:
struct A { ... };
};
If A is not a type, the code should not compile.
This topic is closed to new replies.
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