CODEWITHSUNDEEP
c++
FrozenHeart
FrozenHeart

Reputation: 20726

Different behavior of compilers - template template argument

Suppose i have the following code:

template <template <typename> class T>
class A {};

template <typename T>
class B
{
    A<B> instance;
};

int main()
{
   B<int> instance;
}

gcc 4.7.2 and gcc 4.8.0 compiles this code ok, while icc 13.0.1 and clang 3.2 gave me an error (clang require ::B instead of B, while icc also require whitespace after < in template instantiaion).

Who's right?

I found the thread about it (Template class that refers to itself as a template template parameter?), but i can't understand 14.6.1/2 of the standard and also saw LLVM bug 14350 (http://www.mail-archive.com/[email protected]/msg21095.html). So, clang and intel wrong here?

Upvotes: 0

Views: 72

Answers (1)

rici
rici

Reputation: 241671

14.6.1 says:

The injected-class-name can be used as a template-name or a type-name. When it is used with a template-argument-list, as a template-argument for a template template-parameter, or as the final identifier in the elaborated-type-specifier of a friend class template declaration, it refers to the class template itself.

The "injected-class-name" is the name of the class template (B) "injected" into the scope of the class. In other words, it refers to the use of the unqualified name B within the definition of the class B. If you use that name in a context where a template name is required: i.e., with explicit template arguments (B<int>) or as a template argument for a template which takes a template template parameter (A<B>), it should refer to the template itself.

So, gcc is right.

Also, in C++11, you should not need a space after the < in <::B>. According to section 2.5, paragraph 3, when dividing the input stream into tokens:

if the next three characters are <:: and the subsequent character is neither : nor >, the < is treated as a preprocessor token by itself and not as the first character of the alternative token <:. (<: is another way of writing [.)

Upvotes: 1

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