مسارات IEnumerable<T> والتنفيذ المؤجل

فكرة خط أنابيب LINQ

Where + Select

using System;
using System.Linq;

public class Program
{
  public static void Main(string[] args)
  {
    int[] numbers = new int[] { 1, 2, 3, 4, 5 };

    // Build pipeline: keep even numbers, then square them
    var query = numbers
      .Where(n => n % 2 == 0)
      .Select(n => n * n);

    foreach (int x in query)
    {
      Console.WriteLine(x); // 4, 16
    }
  }
}

تأثير التنفيذ المؤجل

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

public class Program
{
  public static void Main(string[] args)
  {
    List<int> data = new List<int>();
    data.Add(1);
    data.Add(2);

    var evens = data.Where(x => x % 2 == 0); // query is not executed yet

    data.Add(3);
    data.Add(4); // modify source after building query

    foreach (int e in evens)
    {
      Console.WriteLine(e); // prints 2 and 4 because execution is deferred
    }
  }
}

التجسيد (ToList)

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

public class Program
{
  public static void Main(string[] args)
  {
    List<string> words = new List<string>();
    words.Add("apple");
    words.Add("banana");

    var longOnes = words.Where(w => w.Length >= 6);
    List<string> snapshot = longOnes.ToList(); // materialize now

    words.Add("pear");     // changes after materialization
    words.Add("cherry");   // length 6, but snapshot is already frozen

    foreach (string w in snapshot)
    {
      Console.WriteLine(w); // prints "banana" only
    }
  }
}

OrderBy + Take

using System;
using System.Linq;

public class Program
{
  public static void Main(string[] args)
  {
    int[] nums = new int[] { 5, 1, 4, 2, 3 };

    var firstTwoSortedSquares = nums
      .OrderBy(n => n)   // 1,2,3,4,5
      .Select(n => n * n)
      .Take(2);          // 1,4

    foreach (int x in firstTwoSortedSquares)
    {
      Console.WriteLine(x);
    }
  }
}

نصائح وملاحظات مهمة

قاعدة التنفيذ المؤجل

مراجعة