if template class<T> T=int&, why method set(const T val) !== set(const int& val)? const ignored why

T=int&, why .set(const T val) !== .set(const int& val)?

template <class T>
struct ClassA{
public:
    T data;                   // T == int&;
public:
    void set(const T val){    // T == int&;  why !== set(const int& val)
       this->data = val;
    }
};


void main(){
    int num = 1;
    ClassA<int&> instance {num};
    const int val = 100;
    instance.set(val);  // gcc error: binding reference of type 'int&' to 'const int' discards qualifiers
}

I don’t know what the rules on this site are; https://en.cppreference.com/w/cpp/language

>Solution :

[dcl.ref] … Cv-qualified references are ill-formed except when the
cv-qualifiers are introduced through the use of a typedef-name
([dcl.typedef], [temp.param]) or decltype-specifier
([dcl.type.simple]), in which case the cv-qualifiers are ignored

When T is a reference, like your int &, const T is also int &. The const is ignored.

You may have a reference to something that is const or volatile, but the reference itself cannot be const or volatile.