Shows how queries can be reused : Deferred Query « LINQ « C# / CSharp Tutorial

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C# / CSharp Tutorial » LINQ » Deferred Query 
22.76.3.Shows how queries can be reused
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

public class MainClass {
    public static void Main() {
        int[] numbers = new int[] { 541398672};
        var lowNumbers =
            from n in numbers
            where n <= 3
            select n;

        Console.WriteLine("First run numbers <= 3:");
        foreach (int n in lowNumbers) {
            Console.WriteLine(n);
        }

        for (int i = 0; i < 10; i++) {
            numbers[i= -numbers[i];
        }

        Console.WriteLine("Second run numbers <= 3:");
        foreach (int n in lowNumbers) {
            Console.WriteLine(n);
        }
    }
}
22.76.Deferred Query
22.76.1.Deferred Query Execution: shows how query execution is deferred until the query is enumerated at a foreach statement.
22.76.2.How queries can be executed immediately with operators such as ToList().
22.76.3.Shows how queries can be reused
22.76.4.Deferred Query Execution
22.76.5.Immediate Query Execution
22.76.6.A deferred execution query is reevaluated when you reenumerate:
22.76.7.most query operators is that they execute not when constructed, but when enumerated
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