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Reputation: 753

Merging arrays of different sizes with user-implemented zip function

Trying the following code (found here):

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

namespace ConsoleApplication1
{
    class Program
    {
        static void Main()
        {
            var a = new List<int> { 1, 2, 3 };
            var b = new List<int> { 1, 2, 3, 4, 5 };

            var xxx = a.Merge(b, (x, y) => x + y);

            foreach (var c in xxx)
            {
                Console.WriteLine(c);
            }
        }
        static IEnumerable<T> Merge<T>(this IEnumerable<T> first,
                IEnumerable<T> second, Func<T, T, T> operation)
        {
            using (var iter1 = first.GetEnumerator())
            using (var iter2 = second.GetEnumerator())
            {
                while (iter1.MoveNext())
                {
                    if (iter2.MoveNext())
                    {
                        yield return operation(iter1.Current, iter2.Current);
                    }
                    else
                    {
                        yield return iter1.Current;
                    }
                }
                while (iter2.MoveNext())
                {
                    yield return iter2.Current;
                }
            }
        }
    }
}


I get this error:

'System.Collections.Generic.List' does not contain a definition for 'Merge' and no extension method 'Merge' accepting a first argument of type 'System.Collections.Generic.List could be found (are you missing a using directive or an assembly reference?)

Which makes sense. But since I am not sure on how the code should work and I want to fully understand it...

How to fix this problem?

Upvotes: 1

Views: 245

Answers (2)

Hari Prasad
Hari Prasad

Reputation: 16956

Move your extension method to separate static class. 

public static class Extensions
{
    public static IEnumerable<T> Merge<T>(this IEnumerable<T> first,
                IEnumerable<T> second, Func<T, T, T> operation)
    {
         using (var iter1 = first.GetEnumerator())
         using (var iter2 = second.GetEnumerator())
         {
             while (iter1.MoveNext())
             {
                 if (iter2.MoveNext())
                 {
                     yield return operation(iter1.Current, iter2.Current);
                 }
                 else
                 {
                     yield return iter1.Current;
                 }
             }
             while (iter2.MoveNext())
             {
                 yield return iter2.Current;
             }
         }
     }
}

You can find working fiddler sample here

Upvotes: 1

Alexei Levenkov
Alexei Levenkov

Reputation: 100527

Extension must be defined in static class - https://msdn.microsoft.com/en-us/library/bb311042.aspx.

Fix: make sure your Program class that contains Main is static.

static  class Program
{
    private static void Main() ....

Note: proper fix would be to move the Merge extension method to separate static class in the same namespace or other namespace that is included with using.

Upvotes: 3

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