c# – 为什么使用`Delegate.CreateDelegate`创建的Delegate比lam

现在我决定测试速度有多慢,而且令我惊讶的是,使用反射创建的委托实际上大约是使用lambda创建的委托的两倍,而且,令人惊讶的是,大约比使用声明方法的委托快四倍.

看代码

这是一个自定义类,其属性get方法将在委托中使用：

#class to test
class SomeClass
{
    public SomeClass A { get; set; } //property to be gotten
    public static SomeClass GetA(SomeClass c) { return c.A; } //declared getter method
}

这是我测试的三位代表：

PropertyInfo AProp = typeof(SomeClass).GetProperty("A");

//1 - Created with reflection
Func<SomeClass,SomeClass> Getter = (Func<SomeClass,SomeClass>)Delegate.CreateDelegate(typeof(Func<SomeClass,SomeClass>),null,AProp.GetGetMethod());

//2 - Created with a lambda expression
Func<SomeClass,SomeClass> Getter2 = c => c.A;

//3 - Created from a declared method
Func<SomeClass,SomeClass> Getter3 = SomeClass.GetA;

这些是测试：

SomeClass C = new SomeClass();
C.A = new SomeClass(); //test doesn't change whether A is set or null
Stopwatch w;

//reflection delegate
w = Stopwatch.StartNew();
for (int i = 0; i < 10000000; i++) { SomeClass b = Getter(C); }
w.Stop(); Console.WriteLine(w.Elapsed);

//lambda delegate
w = Stopwatch.StartNew();
for (int i = 0; i < 10000000; i++) { SomeClass b = Getter2(C); }
w.Stop(); Console.WriteLine(w.Elapsed);

//method delegate
w = Stopwatch.StartNew();
for (int i = 0; i < 10000000; i++) { SomeClass b = Getter3(C); }
w.Stop(); Console.WriteLine(w.Elapsed);

//no delegate
w = Stopwatch.StartNew();
for (int i = 0; i < 10000000; i++) { SomeClass b = C.A; }
w.Stop(); Console.WriteLine(w.Elapsed);

结果如下：

我也尝试颠倒测试顺序,看是否有影响,或者手表是否以某种方式欺骗我,但不是,测试是一致的.

编辑：考虑“发布”编译,建议：

现在……我原本预计lambda会变慢