Welcome

Hello and welcome. 0:05 I'm Jeremy, in this workshop, 0:06 we'll see how to use generics to create our own types of data structures. 0:08 Data structures are classes that help to organize and use data efficiently. 0:13 For example, lists and dictionary are data structures provided by the .Net Framework. 0:17 The .Net Framework refers to these data structures as collections 0:21 because they're used to organize collections of things. 0:26 List and dictionary are also examples of generic classes. 0:29 You probably remember from previous courses that we can specify 0:34 what type of object we want a list to contain by putting the name of the type 0:38 between these two angle brackets when we instantiate the list. 0:42 This is called the generic type parameter. 0:46 And it's what makes list a generic class. 0:49 We use generic classes like list all the time, but in order to really understand 0:52 how generics and collections work, it's best to implement our own. 0:56 In fact, writing your own data structures to help you work with 1:00 data can help keep your code clean and readable. 1:03 You'll find that data structures you write to help you solve one problem 1:06 can often be reused the next time you run into a similar problem. 1:10 Coding them as generic classes makes them even more usable. 1:14 Let's start writing our own generic data structure. 1:19 I'll be writing the code for this workshop using Visual Studio. 1:22 If you're new to Visual Studio, you can get familiar with it by 1:27 following the link to the tree house workshop in the teacher's notes. 1:30 Of course, you don't have to use Visual Studio to code in C-sharp. 1:34 You can use any editor you want or 1:36 even open a Treehouse workspace by clicking on the button on this page. 1:39 Let's get going. 1:43 I'm in Visual Studio and I've created a console application project. 1:45 I've named this project GenericsDemo. 1:49 In program.cs, I've created four different collections of integers, 1:52 two lists, a HashSet and an array. 1:57 Let's say we wanted to count all of the odd 2:00 numbers contained in these four collections. 2:03 How could we do that? 2:06 I've already written a method to determine if a value is odd or not. 2:07 Now for each collection, we can loop through each value in the array and 2:11 check if it's odd. 2:16 We'll increment a counter for each odd number we find. 2:17 Let's see what the code for this looks like. 2:20 So I'll start by making an integer variable and 2:24 I'll name it numOdd, I'll set it equal to 0. 2:28 This will help us keep track of how many odd numbers we've encountered. 2:34 Now I'll say, foreach var value in list1. 2:38 If, and then we'll call the IsOdd method and pass in value. 2:49 So if it's odd, we'll increment numOdd, so I'll say numOdd ++. 2:56 Now we just need to do this with the other three collections. 3:05 So I'll copy this code, And 3:08 I'll paste it and each time, I'll change it to the next collection name. 3:13 So this one will be list2. 3:17 I'm going to do this two more times. 3:25 So this one is for set1. 3:27 And the last one is for array1. 3:35 There we go. 3:44 So this code loops through each collection and 3:45 increments numOdd for each odd number that it finds. 3:48 We could do anything we wanted with each value in these collections. 3:52 But we'd have to repeat it inside of each loop. 3:56 There's got to be a better way. 3:58 We could shorten the substantially using LINQ. 4:00 If you're unfamiliar with LINQ, 4:04 you'll find a link to a great course about it in the teacher's notes. 4:05 So to use LINQ, I'll first have to go up here and add a using directive. 4:09 So I'll say using System.LINQ. 4:13 This allows us access to all of the extension methods defined in LINQ. 4:19 Now it's write our LINQ expression. 4:25 Our LINQ expression will replace all of these foreach loops. 4:31 So I'll just say numOdd equals list1.Count. 4:34 So here I'll write a lambda expression where x is the value. 4:42 So say x, for each x call IsOdd and pass an x. 4:46 We'll call Count on each collection and add up the results. 4:56 So this is for list2. 5:02 And set1, 5:07 And array1. 5:15 That's certainly less code, but 5:18 we're still repeating the calls to count and IsOdd four times. 5:21 What we'd really like to be able to do is loop through these collections 5:25 as if they're all one collection. 5:29 It's not unreasonable to think that this is something that would be useful for 5:32 more than just this case. 5:35 So we should write some code that does this in a reusable way. 5:37 To do this, we'll write our own data structure that takes a bunch of 5:42 collections and makes them behave like a single collection. 5:45 We can make it a generic collection so that it can be used for 5:49 not just integers, but any type of object that a collection can contain. 5:52 We'll call this new collection type and an enumerable composite. 5:57 And we'll start coding it in the next video. 6:01 While we make this new collection type, we'll also be learning the ins and 6:03 outs of generics as well as how to implement the IEnumerable interface. 6:07 IEnumerable is the interface that every collection type implements. 6:12