const_template.cpp

template <typename T>
struct Foo {
    T *x;
    
    Foo(T *x) : x(x) {}
    
    // operator Foo<const T> () const { return Foo<const T>(x); }
};

template <typename T>
T func(Foo<const T> f, T *out) {
    *out = *f.x;
}

template <typename T>
void wrapper(const T * const x, T *out) {
    Foo<const T> f = {x};
    func(f, out);
}

void library() {
    const double x = 5;
    double out;
    wrapper(&x, &out);
}

int main(int argc, char **argv) {
    double x = 0.0;
    Foo<double> f = {&x};
    double out;
    
    func<double>(f, &out);
    
    library();
    
    return 0;
}