Does the sizeof operator cause template arguments to be deactivated?

Question

I know that the operator sizeofdoes not evaluate its expression argument to get an answer. But this is not one of the non-deductible contexts for patterns. Therefore, I wonder how it interacts with templates and specifically subtracts template arguments. For example, the following are taken from C ++ templates: Complete Guide:

template<typename T> 
class IsClassT { 
  private: 
    typedef char One; 
    typedef struct { char a[2]; } Two; 
    template<typename C> static One test(int C::*); 
    template<typename C> static Two test(...); 
  public: 
    enum { Yes = sizeof(IsClassT<T>::test<T>(0)) == 1 }; 
    enum { No = !Yes }; 
};

This type function determines how its name indicates whether the template argument is a class type. The mechanism is essentially the following condition:

sizeof(IsClassT<T>::test<T>(0)) == 1

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static Two test(...);

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Answer 1

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template< int N> class A {};
template<typename T> void f(A<sizeof(T)>);
f(A<4>());

T sizeof(T)==4.

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