相关疑难解决方法(0)

考虑以下对集合的简单操作:

static List<int> x = new List<int>() { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
var result = x.Where(i => i % 2 == 0).Where(i => i > 5);

现在让我们使用表达式.以下代码大致相当:

static void UsingLambda() {
    Func<IEnumerable<int>, IEnumerable<int>> lambda = l => l.Where(i => i % 2 == 0).Where(i => i > 5);
    var t0 = DateTime.Now.Ticks;
    for (int j = 1; j < MAX; j++) 
        var sss = lambda(x).ToList();

    var tn = DateTime.Now.Ticks;
    Console.WriteLine("Using lambda: {0}", tn …

我正在生成一个表达式树,它将属性从源对象映射到目标对象,然后编译为a Func<TSource, TDestination, TDestination>并执行.

这是结果的调试视图LambdaExpression:

.Lambda #Lambda1<System.Func`3[MemberMapper.Benchmarks.Program+ComplexSourceType,MemberMapper.Benchmarks.Program+ComplexDestinationType,MemberMapper.Benchmarks.Program+ComplexDestinationType]>(
    MemberMapper.Benchmarks.Program+ComplexSourceType $right,
    MemberMapper.Benchmarks.Program+ComplexDestinationType $left) {
    .Block(
        MemberMapper.Benchmarks.Program+NestedSourceType $Complex$955332131,
        MemberMapper.Benchmarks.Program+NestedDestinationType $Complex$2105709326) {
        $left.ID = $right.ID;
        $Complex$955332131 = $right.Complex;
        $Complex$2105709326 = .New MemberMapper.Benchmarks.Program+NestedDestinationType();
        $Complex$2105709326.ID = $Complex$955332131.ID;
        $Complex$2105709326.Name = $Complex$955332131.Name;
        $left.Complex = $Complex$2105709326;
        $left
    }
}

清理它将是:

(left, right) =>
{
    left.ID = right.ID;
    var complexSource = right.Complex;
    var complexDestination = new NestedDestinationType();
    complexDestination.ID = complexSource.ID;
    complexDestination.Name = complexSource.Name;
    left.Complex = complexDestination;
    return left;
}

这是映射这些类型的属性的代码:

public class NestedSourceType
{
  public int ID …

我写了一个复制公共属性的简单对象复制器.我无法弄清楚为什么Dynamic方法比c#版本慢得多.

持续时间

C#方法:4,963毫秒

动态方法:19,924毫秒

请注意 - 当我在启动秒表之前运行动态方法时 - 持续时间不包括编译阶段.我在调试和发布模式下,在x86和x64模式下运行,从VS和命令行运行,结果大致相同(动态方法慢400%).

        const int NBRECORDS = 100 * 1000 * 1000;

        public class Person
        {
            private int mSomeNumber;

            public string FirstName { get; set; }
            public string LastName { get; set; }
            public DateTime DateOfBirth { get; set; }
            public int SomeNumber
            {
                get { return mSomeNumber; }
                set { mSomeNumber = value; }
            }
        }

        public static Action<T1, T2> CreateCopier<T1, T2>()
        {
            var meth = new DynamicMethod("copy", null, new Type[] { typeof(T1), …