Map in ruby and C#

20 April 2008

Using C# 3.0's new extension methods, it's now possible to implement Map, which is pretty awesome.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace FunctionalMap
{
    static class Program
    {
        static IEnumerable<U> Map<T, U>(this IEnumerable<T> s, Func<T, U> f)
        {
            foreach (var item in s)
                yield return f(item);
        }
        static int SumOfSquares(IEnumerable nums)
        {
            return nums.Map(delegate(int x) { return x*x; }).Sum();
            //return nums.Map(x => x * x).Sum();  // <== same as above
        }
        static void Main(string[] args)
        {
            int[] xs = new int[] { 1, 2, 3, 4, 5 };
            Console.WriteLine(Program.SumOfSquares(xs));
            Console.ReadLine();
            return;
        }
    }
}

The Sum() function is a built-in extension, while Map is one you'd add yourself. The this in front of the first parameter signifies an extension method.

In Ruby, the situation is the opposite: map (alias for collect) is built-in, but sum isn't.


sum = 0
xs = [1,2,3,4,5]
xs.map { |n| n*n }.each { |n| sum += n }
puts sum


The C# version requires more syntax but it's a welcome addition that I hope we end up using at work soon.