C++ template typename 和 class 的区别

在比较基础的情况，typename 和 class 是可以交换的，也就是没什么差别：

template<class T>
class Foo
{
};

和

template<typename T>
class Foo
{
};

是等价的。
但也意味着，有些特殊的情况typename和 class 是有区别的。

The first one is in the case of dependent types. typename is used to declare when you are referencing a nested type that depends on another template parameter, such as the typedef in this example:

template
class Foo
{
typedef typename param_t::baz sub_t;
};
The second one you actually show in your question, though you might not realize it:

template < template < typename, typename > class Container, typename Type >
When specifying a template template, the class keyword MUST be used as above -- it is not interchangeable with typename in this case (note: since C++17 both keywords are allowed in this case).

You also must use class when explicitly instantiating a template:

template class Foo;
I'm sure that there are other cases that I've missed, but the bottom line is: these two keywords are not equivalent, and these are some common cases where you need to use one or the other.