Adds Join method

ShittyLINQ/Join.cs

@@ -0,0 +1,38 @@
+using System;
+using System.Collections.Generic;
+
+namespace ShittyLINQ
+{
+    public static partial class Extensions
+    {
+        public static IEnumerable<TResult> Join<TOuter, TInner, TKey, TResult>(this IEnumerable<TOuter> outer,
+            IEnumerable<TInner> inner,
+            Func<TOuter, TKey> outerKeySelector,
+            Func<TInner, TKey> innerKeySelector,
+            Func<TOuter, TInner, TResult> resultSelector)
+        {
+            if (outer == null || outerKeySelector == null || innerKeySelector == null || resultSelector == null) throw new ArgumentNullException();
+            var outerIterator = outer.GetEnumerator();
+
+            var comparer = EqualityComparer<TKey>.Default;
+            TOuter currentOuter = outerIterator.Current;
+
+            while (outerIterator.MoveNext())
+            {
+                currentOuter = outerIterator.Current;
+                TInner currentInner;
+                var innerIterator = inner.GetEnumerator();
+
+                // Find match from inner
+                while (innerIterator.MoveNext())
+                {
+                    currentInner = innerIterator.Current;
+                    if (comparer.Equals(outerKeySelector(currentOuter), innerKeySelector(currentInner)))
+                    {
+                        yield return resultSelector(currentOuter, currentInner);
+                    }
+                }
+            }
+        }
+    }
+}

ShittyLinqTests/JoinTests.cs

@@ -0,0 +1,61 @@
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using ShittyLINQ;
+using System;
+using System.Collections.Generic;
+
+namespace ShittyTests
+{
+    [TestClass]
+    public class JoinTests
+    {
+        class Person
+        {
+            public string Name { get; set; }
+        }
+
+        class Pet
+        {
+            public string Name { get; set; }
+            public Person Owner { get; set; }
+        }
+
+        [TestMethod]
+        public void Join_PerformsJoinOperation()
+        {
+            Person magnus = new Person { Name = "Hedlund, Magnus" };
+            Person terry = new Person { Name = "Adams, Terry" };
+            Person charlotte = new Person { Name = "Weiss, Charlotte" };
+
+            Pet barley = new Pet { Name = "Barley", Owner = terry };
+            Pet boots = new Pet { Name = "Boots", Owner = terry };
+            Pet whiskers = new Pet { Name = "Whiskers", Owner = charlotte };
+            Pet daisy = new Pet { Name = "Daisy", Owner = magnus };
+
+            List<Person> people = new List<Person> { magnus, terry, charlotte };
+            List<Pet> pets = new List<Pet> { barley, boots, whiskers, daisy };
+
+            // Create a list of Person-Pet pairs where 
+            // each element is an anonymous type that contains a
+            // Pet's name and the name of the Person that owns the Pet.
+            var query =
+                people.Join(pets,
+                            person => person,
+                            pet => pet.Owner,
+                            (person, pet) =>
+                                new { OwnerName = person.Name, Pet = pet.Name })
+                                .ToList();
+
+            Assert.AreEqual("Hedlund, Magnus", query[0].OwnerName);
+            Assert.AreEqual("Daisy", query[0].Pet);
+
+            Assert.AreEqual("Adams, Terry", query[1].OwnerName);
+            Assert.AreEqual("Barley", query[1].Pet);
+
+            Assert.AreEqual("Adams, Terry", query[2].OwnerName);
+            Assert.AreEqual("Boots", query[2].Pet);
+
+            Assert.AreEqual("Weiss, Charlotte", query[3].OwnerName);
+            Assert.AreEqual("Whiskers", query[3].Pet);
+        }
+    }
+}