You Can Extend ANYTHING With Extension Methods in C#!

in this video we're going to be looking at extension methods in C and you've probably come across these even if you're not familiar with what the term is as the name suggests extension methods allow us to extend different classes so that means that even if we don't own the class it's defined by someone else or even if it's an interface we're able to add new functionality onto that without modifying the base interface or base class that we're interested in now before I jump over to the code just a quick reminder to check that pin comment for a link to my free newsletter and my courses on dome train but that said let's check out the code so as I mentioned extension methods allow us to add new functionality onto other things that we don't necessarily own and the way that we're able to do that is by using static classes with another special keyword called this and by combining the two things we can add new functionality onto other things but I want to start by explaining that extension methods are really what we call syntactic Sugar just to make things look like they belong to something else when in reality they don't because we don't own the other interface or class that we're interested in extending we're technically not adding new functionality into that interface or class but the way that the IDE and the code looks makes it appear that we can do that so I'm going to start by explaining the inverse of what's actually happening and then we can see how the syntax ends up looking afterward and why it makes it nice and readable for us to work with I'm going to start by making a new static class here and I'm going to call it string extensions and what we'll be doing is adding new functionality onto the string type but like I said I'm going to start by showing you what's actually happening if we start by adding a new static method onto here and I'm just going to make it return a string type but this isn't really what's required I'm going to take in another string and this is not going to be an extension method but it will be afterwards once we go through this and I'm just going to give it a name called Nick's cool method you can name it whatever you want but we have to decide what we want our method to do and that's not really important for this example cuz I'll follow up with another one right after that demonstrates the value maybe we could just make this method reverse the string that we pass in so a naive way that we can do this is that we can use Link to go get all the characters from the string reverse them with the link method called reverse then we have an i inumerable of characters and I'll put that to an array and return a new string created from those characters so instead of Nick's cool method we could just call it reverse string and the way that we would use this is pretty simple right we know that if we have a static class and I go use it up here we can go call reverse string so with this code at the top we can go reverse the string called hello world and like I said we're just calling a static class with a static method passing in a string then I'm going to print the result of that string to the console and the result is not really readable but you get the idea this is Hello World backwards now what does this have to do with extension methods well we just created a static method that operates on a string and an extension method is going to do the exact same thing but change the order that we call things it's functionally identical though so let's see how that looks the way that we would call this instead of having the static class string extensions then reverse string is that what we're able to do is take the string itself and get rid of the static class entirely so we would call hello world and then say reverse string you can see that the way that this reads is very interesting we're able to take any string we want and reverse it that's pretty powerful in terms of how it looks because it makes it seem that reverse string is built on to any string that we have but you can see that Visual Studio is saying hey man that doesn't exist you can't call this but the way that we trick it into making it think that is by using extension methods and like I said there's another special keyword that we'll use called this and if we add this onto the method that we have reverse string and we put this string so this is going to make it such that this parameter here this first one string input is the one that we're operating on with the extension method you can see that line one now does comp pile visual studio now sees reverse string as an extension method even if I hover over it you can see that it has an extension method uh it says extension in the parentheses right so visual studio now sees this as a method that's available to us on strings and it doesn't matter what this class is called now I could type this here and you can see that still reverse string is going to work it doesn't care about the static class name that we have here and the requirements that we need to have an extension method are a static class CL we need to be able to have static on the method and then this keyword out the front of the parameter that we want to be able to add the extension method onto so reverse string is kind of boring and I mean we have the option to do that with two lines of code making it into one is kind of a little bit better but what about something more useful I have another example here of the HTTP context if you're making asp.net core web applications and if we wanted to get the base URL of the HTTP context that we're dealing with in our web application we could go build an extension method just like this to get the base URL and you can see the three things that are required static class static method and this keyword out the front and that means that if we have an HTTP context we could Now call get base URL and then inside of here I just have all of this extra code kind of written out onto separate lines but you can see that we end up creating a URL and then returning it back up to the caller and that means that if we had something like an HTTP context that we were dealing with right now might don't actually have access to one so it's not going to work but what we could do is say our context and then we could ask for the base URL from that and this is an extension method again if I highlight over it you can see that Visual Studio was saying extension in parenthesis and just a reminder right that this method is not technically added onto the class it just makes it look like that in visual studio for us it's quite literally the same as being able to pass in an HTTP context into this method called get base URL and to to prove it I can still call this static class with get base URL in our context so I'm still able to do this right like you can see that this is the extension method syntax but this is still allowing us to call it as a static class and a static method so both of these options still exist even when we have this format here and that's just a super quick tutorial on how you can make your own extension methods in C if you're familiar with link and all of the different powerful things we get with that those are extension methods on the I inumerable type and if you're interested in seeing more about how that works you can check out this video next thanks and I'll see you next time