Template partial specialization.

Templ.cpp

template <typename T, typename = void>
struct Foo;

// A
template <typename T>
struct Foo<unique_ptr<T>, typename std::enable_if<std::is_class<T>::value>::type> {...};

// B
template <typename T>
struct Foo<T, typename std::enable_if<std::is_class<T>::value>::type> {...};