Enumerable, C# - rextester

Language: Layout:

//Rextester.Program.Main is the entry point for your code. Don't change it.
//Microsoft (R) Visual C# Compiler version 2.9.0.63208 (958f2354)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

namespace Rextester
{
    public class Program
    {
        public static void Main(string[] args)
        {
            int[] array = new [] { 1, 2, 3, 4 };
            // тут какой то enumerable
            var preEnumerable = array.Select( i => GetSomeInt( i ) );
            
            
            Console.WriteLine(".Select - converting from array to enumerable");
            // тут enumerable, который делает Select из enumerable, то есть GetSomeInt вызовется и тут и там
            IEnumerable<int> enumerable = preEnumerable.Select( i => GetSomeInt( i ) );
            
            DoWork( enumerable );
        }
        
        public static void DoWork( IEnumerable<int> enumerable )
        {
            Console.WriteLine("Checking for null");
            if ( enumerable == null )
            {
                return;
            }
            
            Console.WriteLine(".Contains when element exists");
            bool isElementInEnumerable_True = enumerable.Contains( 3 );
            Console.WriteLine(".Contains when element not exists");
            bool isElementInEnumerable_False = enumerable.Contains( 65 );
            
            Console.WriteLine(".FirstOrDefault when element exists");
            int firstOrDefault = enumerable.FirstOrDefault( i => i == 3 );
        }
        
        public static int GetSomeInt( int i )
        {
            Console.WriteLine("i = " + i);
            
            return i;
        }
    }
}

Show compiler warnings [ + ] Show input
Compilation time: 0,28 sec, absolute running time: 0,13 sec, cpu time: 0,12 sec, average memory usage: 16 Mb, average nr of threads: 3, absolute service time: 0,44 sec