给函数返回值作为移动构造函数

Question

据我所知，如果函数按值返回，则将其视为右值。

但是当我想传递函数返回值以将构造函数作为参数移动时，不会调用移动构造函数而是复制构造函数。

这是我的代码：

#include <stdio.h>
#include <string.h> // strncmp
#include <vector>

#include <iostream>
#include <fstream>
#include <iomanip>

using namespace std;

class apple_t {
  public:
    apple_t( double data2 ) {
      data = &data2;
      cout<<"value constructor"<<endl;
    }
    apple_t( const apple_t& apple ) {
      data = apple.data;
      cout<<"copy constructor"<<endl;
    }
    apple_t( apple_t&& apple ) {
      data = apple.data;
      apple.data = nullptr;
      cout<<"move constructor"<<endl;
    }

    ~apple_t(){ cout<<"apple killed"<<endl;}
  public:
    double* data;
};


apple_t create_apple(){ apple_t apple(apple_t(40.7)); return apple; } 


int main(int argc, char** argv)
{
  apple_t apple1(20.5);
  apple_t apple2(apple1);
  apple_t apple3(move(apple1));// std::move produces an rvalue-reference
  apple_t apple4( create_apple() );
}

输出如下：

value constructor
copy constructor
move constructor
value constructor
apple killed
apple killed
apple killed
apple killed

我期待＆＃34; apple_t apple4（create_apple（））;＆＃34;，应调用移动构造函数而不是普通构造函数＆＃34; apple_t（double data2）＆＃34;。

有人可以帮帮我吗？