Generic Methods

We just saw how we can write stand-alone generic methods 0:00 when we wrote the take method. 0:03 The cool thing about generic methods is that C# 0:05 can infer what the type perimeter is so we don't have to type it here. 0:08 That's one of my favorite things about generic methods, we can use this feature 0:14 to simplify instantiating the EnumerableCompositor Class. 0:19 So, let's go back to EnumerableCompositor.cs. 0:28 First, we'll create another class name, EnumerableCompositor, but 0:32 this time it won't be generic. 0:36 Will also make it a static class since it will only contain static methods. 0:40 So, say static class EnumerableCompositor one 0:45 common pattern is to write a method that takes care of the instantiation for us. 0:54 This is known as a factory method. 0:59 So, save public, static, and it will return and in EnumerableCompositor. 1:01 So, say in EnumerableCompositor the generic one T. 1:07 i will name the method create, since it will be used to 1:16 create an EnumerableCompositor. 1:20 We'll specify the type parameter here and it will accept and IEnumerable 1:24 of T, and will just have it, except an array of IEnumerables. 1:32 We'll call it collections and 1:40 it will return a new instance of EnumerableCompositor and 1:43 we'll just pass in collections here. 1:49 So, this create method is taking an array of collections and then 2:01 passing that array of collections to the constructor of a EnumerableComposite of T. 2:06 To create a new instance and then returning it. 2:12 Now, in main to get and EnumerableCompositor we can change this 2:16 to EnumerableComposite.Create and 2:21 we'll pass in our array of collections. 2:30 So, say new IEnumerable. 2:35 And I'll split this up on two lines we can see it easier. 2:49 And this is an array. 2:54 Because create is a generic method C# was able to infer what the type parameter is. 2:57 However, we lost the ability to use the collection initializer instead we have to 3:04 pass in array of collections we want the EnumerableCompositor to be composed of. 3:10 C# has another neat feature that allows passing 3:15 any number of parameters into a method. 3:19 Back in the create method, 3:22 we can add a params keyword here in front of the collections parameter. 3:23 Now we can go back to where we're calling create. 3:35 Notice that there are no red squiggly lines. 3:38 And we can still pass in an array. 3:41 However, because we added the params keyword, 3:44 we can also just list the collections here as if they're normal parameters. 3:47 The params keyword allows passing in any number of parameters that are of the type 3:56 in the array. 4:01 There's a caveat though, only the last parameter of the method 4:02 can have the params keyword In this case we only have a single 4:06 parameter in the create method and it's an array of a IEnumerable T. 4:11 So when calling create we can pass in as many IEnumerable of T, 4:16 as we want just as if there are normal parameters to the method. 4:20 They all get put in a single array which we can treat just like a regular rate. 4:24 In this case we're just passing the array to the constructor 4:28 of EnumerableCompositor. 4:32 With the static create method we can now create an instance of 4:34 innumerable compositor without specifying the type or using the new keyword word. 4:39 This is so streamlined that we can copy this right into the for each loop. 4:44 EnumerableCompositor dot create is still a lot to type just to wrap 4:58 a bunch of collections. 5:03 So that they can be enumerated as a single collection. 5:05 Let's make it, so that we don't have to type in EnumerableCompositor any more. 5:08 We do that with a using static directive at the top of the file. 5:13 So we can say, using static Generics Demo.EnumerableCompositor. 5:18 This means that we can call static methods in the EnumerableCompositor class 5:28 without prefixing them with the class name. 5:33 So, we can change this to just create. 5:40 But without the class name it's hard to tell what we're creating here. 5:44 Let's just change the name of the create method to EC. 5:48 In Visual Studio, I can do a rename by clicking on it and hitting control RR. 5:53 I'll type in EC here. 5:59 Notice that it also changed back in the method declaration. 6:02 Now, this is all we need to create and new EnumerableCompositor. 6:05 And because in EnumerableCompositor is IEnumerable we can use 6:10 any link method on it. 6:15 So, to count all of the odd integers contained in all of these collections 6:17 we can just do this down here. 6:21 By leveraging the power of IEnumerable, Yield and Generics, 6:37 we've been able to create a very elegant solution 6:42 to a common problem that can be used for any group of collections. 6:45 Now, instead of writing for foreach loops that all have duplicate code in them, 6:50 we've been able to reduce it to a single line of code that's very readable. 6:55 I like the core logic of my code to be as simple and readable as possible, so 7:00 I find myself making lots of methods in classes like these 7:04 to pull out anything that isn't part of the core logic. 7:08 These methods and classes, like the EnumerableCompositor class and 7:12 the EC method, can often be re-used. 7:16 They get added to my toolkit and 7:19 I often find myself using them again in later projects. 7:21 This often means writing custom data structures by implementing IEnumerable or 7:25 another generic interface such as ICollection, IList, ISet or IDictionary. 7:30 All of those interfaces inherit from IEnumerable. 7:35 So, you will use the same principles we've discussed here 7:39 when implementing those interfaces as well, we're not done yet. 7:42 No discussion of generics is complete without learning how to limit 7:46 what can be used as a generic parameter. 7:50 We'll learn about generic constraints in the next video. 7:53