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struct constRef
{
    int const& _t;
    constRef(int const& ro) : _t(ro) {}
    constRef(constRef const& rxo) : _t(rxo._t) {}
 
    int const & t() const { return _t; }
    static constRef Make(int const & t) { return t; }
};
 
struct Ref
{
    int& _t;
    Ref(int& ro) : _t(ro) {}
    Ref(Ref const& rxo) : _t(rxo._t) {}
    operator constRef() const { return constRef(_t); }
 
    int& t() { return _t; }
    static Ref Make(int& t) { return t; }
};
 
 
int main()
{
    int foo = 5;
    Ref foo2(foo);               
    constRef r(foo2);            // non-const -> const         This compiles.
    constRef c(r);               // const -> const             This compiles.
    Ref other = Ref::Make(foo);  // non-const -> non-const     This compiles
    Ref bar(r);                  // const -> non-const         This fails to compile
 
    return 0;
}
 
int& MakeRef(int& t) { return t; }
 
int main2()
{
    int foo = 5;
    const int& r(foo);          // non-const -> const
    const int& c(r);            // const -> const          This compiles.
    int& other = MakeRef(foo);  // non-const -> non-const  This compiles.
    int& bar(r);                // const -> non-const      This fails to compile.
 
    return 0;
}
 

prog.cpp: In function ‘int main()’:
prog.cpp:30:14: error: no matching function for call to ‘Ref::Ref(constRef&)’
prog.cpp:30:14: note: candidates are:
prog.cpp:15:5: note: Ref::Ref(const Ref&)
prog.cpp:15:5: note:   no known conversion for argument 1 from ‘constRef’ to ‘const Ref&’
prog.cpp:14:5: note: Ref::Ref(int&)
prog.cpp:14:5: note:   no known conversion for argument 1 from ‘constRef’ to ‘int&’
prog.cpp: In function ‘int main2()’:
prog.cpp:43:15: error: invalid initialization of reference of type ‘int&’ from expression of type ‘const int’
prog.cpp:41:16: warning: unused variable ‘c’ [-Wunused-variable]
prog.cpp:42:10: warning: unused variable ‘other’ [-Wunused-variable]
prog.cpp:43:10: warning: unused variable ‘bar’ [-Wunused-variable]

Standard output is empty