[.NET 2.0] Testing Generics, Collections and Yield Return

Monday, May 15, 2006

I've not looked too much at the yield return statement in c# 2.0 yet, but if you learn how to use it I'm sure it will become something you use "every day" when programming. Whenever you need to do some conditional iterations on a collection, array or list, yield may be a nice solution to go for. A few, silly and not perfect, snippets which helped me understand how to use yield return:

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

public class Program
{

    static void Main()
    {
        // Build up a few arrays and a list to work with
        string[] names = { "Johan", "Per", "Thomas", "Lina", "Juan", "Jan-Erik", "Mats" };
        int[] values = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 0 };
        List<int> list = new List<int>();
        list.Add(1);
        list.Add(2);
        list.Add(3);
        list.Add(4);

        Console.WriteLine("Get the names which contains an 'a':");

        // Iterate on all names which contains letter 'a'
        foreach (string name in EnumerableUtils<string>.GetNamesContainingLetter(names, 'a'))
        {
            Console.Write("{0} ", name);
        }
        Console.WriteLine();
        Console.WriteLine();

        //iterate through first half of this collection
        Console.WriteLine("First half of the name-array:");
        foreach (string name in EnumerableUtils<string>.GetFirstHalfFromList(names))
        {
            Console.Write("{0} ", name);
        }
        Console.WriteLine();
        Console.WriteLine();

        //iterate through first half of another collection
        Console.WriteLine("First half of the value-array:");
        foreach (int value in EnumerableUtils<int>.GetFirstHalfFromList(values))
        {
            Console.Write("{0} ", value);
        }

        Console.WriteLine();
        Console.WriteLine();

        //iterate through first half of a List
        Console.WriteLine("First half of the value-list:");
        foreach (int value in EnumerableUtils<int>.GetFirstHalfFromList(list))
        {
            Console.Write("{0} ", value);
        }
        
        Console.WriteLine();
    }
}

public class EnumerableUtils<T>
{
    public static IEnumerable GetNamesContainingLetter(string[] names, char letter)
    {
        foreach (string name in names)
        {
            if (name.ToLower().Contains(letter.ToString().ToLower()))
                yield return name;
        }
    }

    public static IEnumerable<T> GetFirstHalfFromList(List<T> arr)
    {
        for (int i = 0; i < arr.Count / 2; i++)
            yield return arr[i];
    }

    public static IEnumerable<T> GetFirstHalfFromList(T[] arr)
    {
        for (int i = 0; i < arr.Length / 2; i++)
            yield return arr[i];
    }
}

No Comments