What is the meaning of the address symbol & in a constructor? - c++

Question

I'm looking up c++ library, and see the istream class, I am confused with a contractor with an address symbol. what is the meaning of a constructor with an address symbol?
one of the istream constructors is.
protected: iostream& (iostream&& x);
I found it in website cplusplus.com,
link: iostream
I defined a customer class with a similar constructor that has a & symbol:
//Test.cpp
#include <iostream>/*cout,cin*/
#include <typeinfo>/*typeid(),name()*/
using namespace std;
struct MyTest{
MyTest&(double b){}
};
int main(int argc,char* argv[]){
MyTest mt2(2.1);
cout << typeid(mt2).name() << endl;
return 0;
}
I use the below command to compile it:
g++ Test.cpp -o Test -std=c++11
however, I get some compile error messages:
Test.cpp:7:11: error: expected unqualified-id before ‘float’
MyTest&(float b){}
^
Test.cpp:7:11: error: expected ‘)’ before ‘float’
Test.cpp:7:10: error: expected ‘;’ at end of member declaration
MyTest&(float b){}
^
Test.cpp:7:17: error: expected ‘;’ at end of member declaration
MyTest&(float b){}
^
Test.cpp:7:18: error: expected unqualified-id before ‘)’ token
MyTest&(float b){}
^
Test.cpp: In function ‘int main(int, char**)’:
Test.cpp:12:16: error: no matching function for call to ‘MyTest::MyTest(double)’
MyTest mt2(2.1);
I got confused, c++ library istream class is fine. why did my custom class constructor fail? what am I missing?

Answer 1

The information on cplusplus.com is... sometimes not dependable. (See What's wrong with cplusplus.com? for a discussion of this.) On CPPReference, you can see that the move constructor is, you know, just a regular move constructor.

Answer 2

This is a bug in http://www.cplusplus.com/reference/istream/iostream/iostream/.
If you look at https://en.cppreference.com/w/cpp/io/basic_iostream/basic_iostream, you will find
protected: basic_iostream( basic_iostream&& other );