By disabling copy constructor and copy assignment, we can be sure that the ownership of B is “moved” from one owner to another.
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| #include <iostream>
#include <memory>
using namespace std;
struct B {
~B() {
puts("~B");
}
};
struct A {
unique_ptr<B> o;
A() {}
explicit A(B* o_) : o{o_} {}
A(const A&) = delete;
A& operator=(const A&) = delete;
A(A&& other) : o{move(other.o)} {
puts("move ctor");
}
A& operator=(A&& other) {
puts("move =");
o = move(other.o);
return *this;
}
};
int main()
{
{
A a1{new B};
printf("a1.o is %p\n", a1.o.get());
}
puts("");
{
A a1{new B};
printf("a1.o is %p\n", a1.o.get());
A a2 = move(a1);
printf("a1.o is %p\n", a1.o.get());
}
puts("");
{
A a1{new B};
printf("a1.o is %p\n", a1.o.get());
A a2{move(a1)};
printf("a1.o is %p\n", a1.o.get());
}
puts("");
{
A a1{new B};
printf("a1.o is %p\n", a1.o.get());
A a2;
a2 = move(a1);
printf("a1.o is %p\n", a1.o.get());
}
return 0;
}
|
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| $ clang++ -std=c++11 -stdlib=libc++ test.cc && ./a.out
a1.o is 0x189cc20
~B
a1.o is 0x189cc20
move ctor
a1.o is (nil)
~B
a1.o is 0x189cc20
move ctor
a1.o is (nil)
~B
a1.o is 0x189cc20
move =
a1.o is (nil)
~B
|