复制-交换习语的低效率

#include <algorithm>
#include <iostream>
#include <vector>
using namespace std;
class X
{
public:
    X()
    {
    }
    explicit X(const size_t initialCapacity)
    {
        m_v.reserve(initialCapacity);
    }
    X(const X& other)
        : m_v(other.m_v)
    {
    }
    X(X&& other)
        : m_v(move(other.m_v))
    {
    }
    void SetV(const vector<double>& v)
    {
        m_v = v;
    }
    const vector<double>& GetV() const
    {
        return m_v;
    }
#ifdef TEST_COPY_AND_SWAP     
    //
    // Implement a unified op= with copy-and-swap idiom.
    //
    X& operator=(X other)
    {
        swap(*this, other);       
        return *this;
    }
    friend void swap(X& lhs, X& rhs)
    {
        using std::swap;
        swap(lhs.m_v, rhs.m_v);
    }    
#else    
    //
    // Implement copy op= and move op= separately.
    //
    X& operator=(const X& other)
    {
        if (this != &other)
        {
            m_v = other.m_v;
        }
        return *this;
    }
    X& operator=(X&& other)
    {
        if (this != &other)
        {
            m_v = move(other.m_v);
        }
        return *this;
    }    
#endif
private:
    vector<double> m_v;
};    
// Test vector assignment from a small vector to a vector with big capacity.
void Test1()
{
    vector<double> v1;
    v1.reserve(1000*1000);
    vector<double> v2(1000);
    cout << "v1.capacity() = " << v1.capacity() << 'n';
    cout << "v2.capacity() = " << v2.capacity() << 'n';
    v1 = v2;
    cout << "nAfter copy v1 = v2:n";    
    cout << "v1.capacity() = " << v1.capacity() << 'n';
    cout << "v2.capacity() = " << v2.capacity() << 'n';
}    
// Similar to Test1, but now vector is a data member inside a class.
void Test2()
{
#ifdef TEST_COPY_AND_SWAP 
    cout << "[Copy-and-swap]nn";
#else
    cout << "[Copy-op= and move-op=]nn";
#endif
    X x1(1000*1000);
    vector<double> v2(1000);
    X x2;
    x2.SetV(v2);
    cout << "x1.GetV().capacity() = " << x1.GetV().capacity() << 'n';
    cout << "x2.GetV().capacity() = " << x2.GetV().capacity() << 'n';
    x1 = x2;
    cout << "nAfter x1 = x2:n";
    cout << "x1.GetV().capacity() = " << x1.GetV().capacity() << 'n';
    cout << "x2.GetV().capacity() = " << x2.GetV().capacity() << 'n';
}
int main()
{
    Test1();       
    cout << 'n';    
    Test2();
}