我以为lambda functions
, delegates
and anonymous functions
具有相同的主体将具有相同的“速度”,但是,运行以下简单的程序:
static void Main(string[] args)
{
List<int> items = new List<int>();
Random random = new Random();
for (int i = 0; i < 10000000; i++)
{
items.Add(random.Next());
}
Stopwatch watch;
IEnumerable<int> result;
Func<int, bool> @delegate = delegate(int i)
{
return i < 500;
};
watch = Stopwatch.StartNew();
result = items.Where(@delegate);
watch.Stop();
Console.WriteLine("Delegate: {0}", watch.Elapsed.TotalMilliseconds);
Func<int, bool> lambda = i => i < 500;
watch = Stopwatch.StartNew();
result = items.Where(lambda);
watch.Stop();
Console.WriteLine("Lambda: {0}", watch.Elapsed.TotalMilliseconds);
watch = Stopwatch.StartNew();
result = items.Where(i => i < 500);
watch.Stop();
Console.WriteLine("Inline: {0}", watch.Elapsed.TotalMilliseconds);
Console.ReadLine();
}
I get:
代表:4.2948 毫秒
拉姆达:0.0019 毫秒
匿名:0.0034 毫秒
尽管可以忽略不计,但为什么这三种看似相同的方法以不同的速度运行?幕后发生了什么?
Update:
正如评论所建议的,以下“强制”Where
通过致电ToList()
在上面。此外,还添加了一个循环以提供更多运行数据:
while (true)
{
List<int> items = new List<int>();
Random random = new Random();
for (int i = 0; i < 10000000; i++)
{
items.Add(random.Next());
}
Stopwatch watch;
IEnumerable<int> result;
Func<int, bool> @delegate = delegate(int i)
{
return i < 500;
};
watch = Stopwatch.StartNew();
result = items.Where(@delegate).ToList();
watch.Stop();
Console.WriteLine("Delegate: {0}", watch.Elapsed.TotalMilliseconds);
Func<int, bool> lambda = i => i < 500;
watch = Stopwatch.StartNew();
result = items.Where(lambda).ToList();
watch.Stop();
Console.WriteLine("Lambda: {0}", watch.Elapsed.TotalMilliseconds);
watch = Stopwatch.StartNew();
result = items.Where(i => i < 500).ToList();
watch.Stop();
Console.WriteLine("Inline: {0}", watch.Elapsed.TotalMilliseconds);
Console.WriteLine(new string('-', 12));
}
上述代码的结果是每个函数大约需要 120 毫秒。