将 ValueTuple 转换为 IEnumerable

Question

是否有更明智的方法来执行以下操作：

public static class ValueTupleAdditions {
  public static IEnumerable<object> ToEnumerable<A, B>(this ValueTuple<A, B> tuple) {
    yield return tuple.Item1;
    yield return tuple.Item2;
  }
  public static IEnumerable<object> ToEnumerable<A, B, C>(this ValueTuple<A, B, C> tuple) {
    yield return tuple.Item1;
    yield return tuple.Item2;
    yield return tuple.Item3;
  }

  [etc]
}

编辑：既然人们要求一个用例，那就给你。

using Xunit;

namespace Whatever {

  public class SomeTestClass {
    public static IEnumerable<(string, Expression<Func<string, string>>, string)> RawTestData() {
      yield return ("Hello", str => str.Substring(3), "lo");
      yield return ("World", str => str.Substring(0, 4), "worl");
    }
    public static IEnumerable<object[]> StringTestData() {
      return RawTestData().Select(vt => new object[] { vt.Item1, vt.Item2, vt.Item3 });
       // would prefer to call RawTestData().Select(vt => vt.ToArray()) here, but it doesn't exist.
    }

    [Theory, MemberData(nameof(StringTestData))]
    public void RunStringTest(string input, Expression<Func<string, string>> func, string expectedOutput) {
      var output = func.Compile()(input);
      Assert.Equal(expectedOutput, output);
    }
  }
}

Answer 1

一种方法是使用基于ITuple的扩展方法，另见answer by Julien Couvreur：

public static IEnumerable<T> ToEnumerable<T>( this ITuple tuple ) {
    for ( var n = 0; n < tuple.Length; n++ ) yield return (T)tuple[ n ];
}

示例用法：

var directions = (
    right: (cx: 1, cy: 0),
    down: (cx: 0, cy: 1),
    left: (cx: -1, cy: 0),
    up: (cx: 0, cy: -1)
);
foreach ( var direction in directions.ToEnumerable<(int cx, int cy)>() ) {
    var (cx, cy) = direction;
    TryMovePiece( (x + cx, y + cy) );
}

Answer 2

一种方法是通过ITuple interface。

public interface ITuple
{
    int Length { get; }
    object this[int index] { get; }
}

仅在 .NET Core 2.0、Mono 5.0 和 .NET Framework 的下一版本（未发布，4.7 之后）中可用。 它不（也永远不会）通过 ValueTuple 包作为旧框架的附加组件提供。

此 API 旨在供 C# 编译器用于未来的模式工作。

Answer 3

一点反思：

namespace ConsoleApp1
{
    using System;
    using System.Collections.Generic;
    using System.Linq;

    public class Program
    {
        public static void Main()
        {
            var tuple = (1, 2, 3, 4, 5, 6, 7);
            var items = ToEnumerable(tuple);

            foreach (var item in items)
            {
                Console.WriteLine(item);
            }
        }

        private static IEnumerable<object> ToEnumerable(object tuple)
        {
            if (tuple.GetType().GetInterface("ITupleInternal") != null)
            {
                foreach (var prop in tuple.GetType()
                    .GetFields()
                    .Where(x => x.Name.StartsWith("Item")))
                {
                    yield return prop.GetValue(tuple);
                }
            }
            else
            {
                throw new ArgumentException("Not a tuple!");
            }
        }
    }
}