LINQ将函数的结果作为源延迟执行(例如,Console.ReadLine)

如果你不介意一些额外的基础设施,那也不错——你可以创建一个 DeferredEnumerable<T>

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;

// Just for type inference...
public static class DeferredEnumerable
{
    public static IEnumerable<T> For<T>(Func<IEnumerable<T>> func) =>
        new DeferredEnumerable<T>(func);
}

public sealed class DeferredEnumerable<T> : IEnumerable<T>
{
    private readonly Func<IEnumerable<T>> func;

    public DeferredEnumerable(Func<IEnumerable<T>> func)
    {
        this.func = func;
    }

    public IEnumerator<T> GetEnumerator() => func().GetEnumerator();

    IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
}

class Test
{
    static void Main()
    {
        var query = 
            from c in DeferredEnumerable.For(Console.ReadLine)
            group c by char.IsDigit(c) into gr
            select new { IsDigit = gr.Key, Count = gr.Count() };


        Console.WriteLine("First go round");
        Console.WriteLine(string.Join(Environment.NewLine, query));

        Console.WriteLine("Second go round");
        Console.WriteLine(string.Join(Environment.NewLine, query));
    }
}

我找到了两种解决方案,但它们真的很难看,我不想使用它们

解决方案1

static IEnumerable<string> GetDeferredConsoleReadLine()
{
    yield return Console.ReadLine();
}

var query = from line in GetDeferredConsoleReadLine()
            from c in line
            group c by char.IsDigit(c) into gr
            select new { IsDigit = gr.Key, Count = gr.Count() };

yield return 函数的结果。

var query = from line in
                from _ in "1"
                select Console.ReadLine()
            from c in line
            group c by char.IsDigit(c) into gr
            select new { IsDigit = gr.Key, Count = gr.Count() };

有没有其他方法可以做到这一点 SelectMany 在查询中?

您可以将查询放在一个单独的方法中。

static void Main(string[] args)
{
    while (true)
    {
        foreach (var y in RunQuery()) {
            Console.WriteLine($"{y.IsDigit}: {y.Count}");
        }
    }
}

class A{public bool IsDigit { get; set; } public int Count { get; set; } }

private static IEnumerable<A> RunQuery()
{
    return from c in Console.ReadLine()
                group c by char.IsDigit(c) into gr
                select new A { IsDigit = gr.Key, Count = gr.Count() };
}