[Bug c++/55098] New: c++11: move constructor doesn't run at all (but with a hammer)

[lisp2d at lisp2d dot net]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55098



             Bug #: 55098

           Summary: c++11: move constructor doesn't run at all (but with a

                    hammer)

    Classification: Unclassified

           Product: gcc

           Version: 4.7.1

            Status: UNCONFIRMED

          Severity: normal

          Priority: P3

         Component: c++

        AssignedTo: unassig...@gcc.gnu.org

        ReportedBy: lis...@lisp2d.net





standard says:

A non-template constructor for class X is a move constructor if its first

parameter is of type X&&, const

X&&, volatile X&&, or const volatile X&&, and either there are no other

parameters or else all other

parameters have default arguments (8.3.6). [ Example: Y::Y(Y&&) is a move

constructor.

struct Y {

Y(const Y&);

Y(Y&&);

};

extern Y f(int);

Y d(f(1)); // calls Y(Y&&)

Y e = d; // calls Y(const Y&)



test.cpp:

#include    <iostream>

class    A{

public:

int    a;

explicit    A(int    const    &    x):a{x}{std::cout<<"A(int const

&)"<<std::endl;}

A(A    const    &    x):a{x.a}{std::cout<<"A(A const &)"<<std::endl;}

A(A    &&    x):a{x.a}{std::cout<<"A(A &&)"<<std::endl;}

A operator    +(A    const & x){std::cout<<"A+(A const &)"<<std::endl;return

A{a + x.a};}

A operator    +(A    && x){std::cout<<"A+(A &&)"<<std::endl;return A{a + x.a};}

};



extern A    f(int    const    &    x);



int    main(int,char**){

std::cout<<"---"<<std::endl;

A x(f(0));

std::cout<<"---"<<std::endl;

A    y(f(1)+f(2));

std::cout<<"---"<<std::endl;

}



A    f(int    const    &    x){

    A    tmp{x};

    ++    (tmp.a);

    return    tmp;}



result:

---

A(int const &)

---

A(int const &)

A(int const &)

A+(A &&)

A(int const &)

---



The hammer is:

A x(static_cast<A &&>(f(0)));

A y(static_cast<A &&>(f(1)+f(2)));