C++ explicit constructor that takes a pointer

Question

I've recently stumbled across an explicit constructor that receives a single pointer argument. I wonder if the explicit keyword is necessary in this case? as there is no constructor for a pointer so there cannot be any implicit conversion.

class Foo {
 public:
  explicit Foo(int* int_ptr);
}

Answer 1

The following code:

void f(Foo) {}

int main()
{
    int* p;
    f(p);
}

• Fails to compile with explicit.

• Happily compiles without it.

live example on godbolt.org