c++ 11学习笔记--Lambda 表达式（对比测试Lambda ，bind，Function Object）

#include <algorithm>
#include <iostream>
#include <vector>
using namespace std;

int main() 
{
   // Create a vector object that contains 10 elements.
   vector<int> v;
   for (int i = 0; i < 10; ++i) {
      v.push_back(i);
   }

   // Count the number of even numbers in the vector by 
   // using the for_each function and a lambda.
   int evenCount = 0;
   for_each(v.begin(), v.end(),[&evenCount] (int n) {
      cout << n;
      if (n % 2 == 0) {
         cout << " is even " << endl;
         ++evenCount;
      } else {
         cout << " is odd " << endl;
      }
   });

   // Print the count of even numbers to the console.
   cout << "There are " << evenCount 
        << " even numbers in the vector." << endl;
}

#include <algorithm>
#include <iostream>
#include <vector>
using namespace std;

class FunctorClass
{
public:
    // The required constructor for this example.
    explicit FunctorClass(int& evenCount) 
        : m_evenCount(evenCount)
    {
    }

    // The function-call operator prints whether the number is
    // even or odd. If the number is even, this method updates
    // the counter.
    void operator()(int n) const
    {
        cout << n;

        if (n % 2 == 0) {
            cout << " is even " << endl;
            ++m_evenCount;
        } else {
            cout << " is odd " << endl;
        }
    }

private:
    // Default assignment operator to silence warning C4512.
    FunctorClass& operator=(const FunctorClass&);

    int& m_evenCount; // the number of even variables in the vector.
};


int main() 
{
    // Create a vector object that contains 10 elements.
    vector<int> v;
    for (int i = 0; i < 10; ++i) {
        v.push_back(i);
    }

    // Count the number of even numbers in the vector by 
    // using the for_each function and a function object.
    int evenCount = 0;
    for_each(v.begin(), v.end(), FunctorClass(evenCount));

    // Print the count of even numbers to the console.
    cout << "There are " << evenCount 
        << " even numbers in the vector." << endl;
}

#include <cstdint>
#include <chrono>
#include <iostream>
#include <string>
#include <thread>
#include <vector>
#include <algorithm>

#if USE_BOOST
#include <boost/function.hpp>
#include <boost/bind.hpp>
#endif


class FunctorClass
{
public:
    // The required constructor for this example.
    explicit FunctorClass(uint64_t& evenCount)
    : m_evenCount(evenCount)
    {
    }
    
    // The function-call operator prints whether the number is
    // even or odd. If the number is even, this method updates
    // the counter.
    void operator()(int n) const
    {
         m_evenCount += n;
    }
    
private:
    // Default assignment operator to silence warning C4512.
    FunctorClass& operator=(const FunctorClass&);
    
    uint64_t& m_evenCount; // the number of even variables in the vector.
};

class timer
{
public:
    typedef std::chrono::high_resolution_clock clock;
    typedef clock::time_point                  time_point;
    typedef clock::duration                    duration;
    
public:
    timer()
    {
        reset();
    }
    
    void reset()
    {
        _starttime = clock::now();
    }
    
    duration elapsed() const
    {
        return clock::now() - _starttime;
    }
protected:
    time_point _starttime;
};

bool test_timer()
{
    using std::chrono::milliseconds;
    typedef timer::duration duration;
    
    const milliseconds sleep_time(500);
    
    timer t;
    std::this_thread::sleep_for(sleep_time);
    duration recorded = t.elapsed();
    
    // make sure the clock and this_thread::sleep_for is precise within one millisecond (or at least in agreement as to
    // how inaccurate they are)
    return (recorded - milliseconds(1) < sleep_time)
    && (recorded + milliseconds(1) > sleep_time);
}

template <typename T>
void volatile_write(const T& x)
{
    volatile T* p = new T;
    *p = x;
    delete p;
}

template <typename Function>
void run_test(const std::string& name, Function func)
{
    std::cout << name;
    timer t;
    volatile_write(func());
    timer::duration duration = t.elapsed();
    std::cout << ‘\t‘ << duration.count() << std::endl;
}

template <typename Function>
void do_test_loop(Function func, const uint64_t upper_limit = 100000000ULL)
{
    uint64_t i;
    for (i = 0; i < upper_limit; ++i)
        func(i);
    if(i == upper_limit)
    {
        std::cout<<i;
    }
}

uint64_t test_accumulate_lambda()
{
    uint64_t x = 0;
    auto accumulator = [&x] (uint64_t i) { x += i;
 };
    do_test_loop(accumulator);
    return x;
}

void test_accumulate_bind_function(uint64_t& x, uint64_t i)
{
    x += i;
}

uint64_t test_accumulate_bind()
{
    namespace arg = std::placeholders;
    
    uint64_t x = 0;
    std::function<void (uint64_t)> accumulator = std::bind(&test_accumulate_bind_function, std::ref(x), arg::_1);
    do_test_loop(accumulator);
    return x;
}

uint64_t test_accumulate_bound_lambda()
{
    uint64_t x = 0;
    std::function<void (uint64_t)> accumulator = [&x] (uint64_t i) { x += i; };
    do_test_loop(accumulator);
    return x;
}


uint64_t test_accumulate_class_function()
{
    uint64_t x = 0;

    do_test_loop(FunctorClass(x));
   // for_each(v.begin(), v.end(), FunctorClass(x));
    return x;
}

uint64_t test_accumulate_bind_auto()
{
    namespace arg = std::placeholders;
    
    uint64_t x = 0;
    auto accumulator = std::bind(&test_accumulate_bind_function, std::ref(x), arg::_1);
    do_test_loop(accumulator);
    return x;
}

#if USE_BOOST
uint64_t test_accumulate_boost_bind()
{
    uint64_t x = 0;
    
    boost::function<void (uint64_t)> accumulator = boost::bind(&test_accumulate_bind_function, boost::ref(x), _1);
    do_test_loop(accumulator);
    return x;
}

uint64_t test_accumulate_boost_bound_lambda()
{
    uint64_t x = 0;
    boost::function<void (uint64_t)> accumulator = [&x] (uint64_t i) { x += i; };
    do_test_loop(accumulator);
    return x;
}
#endif

int main()
{
    if (!test_timer())
    {
        std::cout << "Failed timer test." << std::endl;
        return -1;
    }
    
    run_test("Accumulate (lambda)            ", &test_accumulate_lambda);
    run_test("Accumulate (bind)              ", &test_accumulate_bind);
    run_test("Accumulate (bound lambda)      ", &test_accumulate_bound_lambda);
    run_test("Accumulate (Function Object)    ", &test_accumulate_class_function);
    run_test("Accumulate (bind auto)    ", &test_accumulate_bind_auto);
#if USE_BOOST
    run_test("Accumulate (boost bind)        ", &test_accumulate_boost_bind);
    run_test("Accumulate (boost bound lambda)", &test_accumulate_bound_lambda);
#endif
}