不建议使用未删除的项目。

例如，给定-Wextra，发出铿锵声15

struct A
{
    A() {}
    A(const A &) {}
};

int main()
{
    A a, b;
    a = b;
}

吐口水

<source>:4:5: warning: definition of implicit copy assignment operator for 'A' is deprecated because it has a user-provided copy constructor [-Wdeprecated-copy-with-user-provided-copy]
    A(const A &) {}
    ^
<source>:10:7: note: in implicit copy assignment operator for 'A' first required here
    a = b;
      ^

同样地，

struct A
{
    A() {}
    A &operator=(const A &) {return *this;}
};

int main()
{
    A a, b(a);
}

给予

<source>:4:8: warning: definition of implicit copy constructor for 'A' is deprecated because it has a user-provided copy assignment operator [-Wdeprecated-copy-with-user-provided-copy]
    A &operator=(const A &) {return *this;}
       ^
<source>:9:10: note: in implicit copy constructor for 'A' first required here
    A a, b(a);
         ^