If I have a template class with a default template type, I have to write the template angle brackets. Is it somehow possible to avoid this?
Example:
template <typename T=int>
class tt {
public:
T get() { return 5; }
};
...
tt<> t; // how to avoid <>
std::cout << t.get() << std::endl;
Until now i've did this by a separate namespace and redeclaring the class:
namespace detail_ {
template <typename T=int>
class tt {
public:
T get() { return 5; }
};
}
class tt : public detail_::tt {}
...
tt t;
std::cout << t.get() << std::endl;
The problem is, if I want to use the class with an other type I have to go over namespace detail_. Is there another solution, which I didn't see yet.
Since C++17, because of class template argument deduction, things have changed.
tt and tt<> are not the same thing: types and class templates were different and continue to be treated differently.
Anyway in simple scenarios like the one in your example, C++17 assumes what you mean and the <> aren't needed anymore.
Further details:
... if I want to use the class ...
This is a common source of confusion. A class template is not a class, but a template from which classes are generated. The angle brackets is what tells the compiler that you want to generate a class out of the class template with the given template arguments, without the angle brackets what you have is a template.
template <typename T = int>
struct TemplateClass {...};
template <template class T<typename> >
void f() {
T<int> t; ...
}
template <typename T>
void g() {
T t; ...
}
f<TemplateClass>(); // Accepts a template with a single type argument
g<TemplateClass<> >(); // Accepts a type, that can be generated out of the template
The language does not allow the coexistence of a template and a type with the same name in the same namespace, so the answer is that it cannot be done. You can create a type alias but you will have to give it a different name.
You can use typedef...
typedef tt<> tt_;
And then simply use tt_.
来源：https://stackoverflow.com/questions/16014736/avoid-angle-brackets-in-default-template