C# Generics - What they are, why they are useful, and how to create them

Have you ever used a List of T and wondered what the T meant? Or maybe you heard the term generics but you did not really know what that was or why it was important. Maybe you have been using generics for a while but didn't know you could create your own. Whatever the case, this video is for you. In this video, I am going to lay the foundation of what generics are and what makes them so powerful. Then, we will look at a demonstration I have set up on how you can keep your code dry, better conform to the SOLID principles, and make your life easier by implementing generics a class.
Source Code: leadmagnets.app/?Resource=CSh...
Patreon: / iamtimcorey
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0:00 - Intro
1:33 - Creating a List of T
4:03 - Why not to use ArrayList and why generics are useful
11:10 - Demo app walk through pt1
22:56 - The problem: repetition
28:55 - Solving the repetition with generics; Demo application walk through pt2
47:50 - When to use generics
50:41 - Passing in more than one type of generic

[@marienoellemaltais]

You are such a great teacher. Many blessings to you. Simplicity is born out of a deeper understanding. Your tutorials are brilliant, like a breath of fresh air.

[@IAmTimCorey]

Thank you for the kind words.

[@ValiRossi]

I agree. Every lesson is very consistent which helps in the learning process.

[@thesophisticatedvelocirapt7320]

"Simplicity is born out of a deeper understanding" .........deep And yes, Tim Corey is the best

[@octavian9168]

Glad you're still with us. Sounds like a crazy experience, that tsunami... Hopefully one day I will learn French or find a translated copy of your book. Interesting to see you coding!

[@LiakatHossain]

And his voice as well 😍

[@NM-tr1ii]

You're my fav C# instructor. Period! I don't know what moment or who sparked the idea in your head that you decided to share your knowledge with the world, I'm just grateful that you did :-)

[@huzaifatinwala]

Best C# generics tutorial I have come across. Thanks, Tim. Really appreciate it.

[@IAmTimCorey]

You are most welcome. Thanks for watching.

[@mannys12345]

Tim, great course. I like the way you explain "why" we would use Generics in real-world scenarios as opposed to just giving us "high-level" examples. Note that this teaching method sets you apart from other teachers. Also, you showed us an example where originally we don't use generics and then where (and why) we would use Generics (code reuse and decoupling logic implementation from actual data types).

[@IAmTimCorey]

I am glad you found it helpful.

[@christianromedahl4456]

Agree. One of the best teachers that I've found so far. Really clear, in-depth, not going on too fast (like some others just rushing on), so it's easy to follow and grasp. Brilliant! Thanx a lot. :)

[@IAmTimCorey]

You are most welcome. Thanks for watching.

[@n9434178]

Thank you Tim! This video improved my understanding of the use of generics.

[@IAmTimCorey]

Excellent!

[@linukkis]

You're hands down the best teacher I've ever seen. Nothing is left unexplained, everything is always very clear and simple to understand. Thank you so much for inspiring other programmers through your awesome videos!

[@IAmTimCorey]

I appreciate the kind words.

[@branislavpetrovic7486]

This is excellent and simple tutorial on C# generics. Thank you for your efforts and sharing your precious knowledge.

[@IAmTimCorey]

I am glad you enjoyed it.

[@forresttucker168]

I had no problems whatsoever understanding why it was done this way and how generics work, and I forsee it saving me a lot of work in the future. Thanks a lot Tim....

[@higherpurpose1212]

what I iike about your tutorials like this one, is you don't over complicate things and I believe you always consider the level of skill of your watchers, explaining how and why things are done in a certain way. thanks Tim.

[@IAmTimCorey]

Glad you like them!

[@rodolfoeliezer1346]

The professor who doesn't assume understanding of some specific part of the explanation makes my understanding much better. Thank you a lot Tim Corey, for providing such a good content and yet free. Thanks from Brazil.

[@IAmTimCorey]

You're very welcome! ... from Texas USA

[@orcaowlwizco369]

Man been watching and liking all your vids. They are solid. As a person finishing up a year's worth of c# classes, I still find your way of teaching really easy to understand, and the tips and way in which you deliver information is extremely helpful. Many thanks buddy!

[@IAmTimCorey]

You are most welcome. Thanks for watching.

[@volo7]

I haven't come across a better teacher for C# programming online. Thank you so much for what you are doing!

[@IAmTimCorey]

You're very welcome!

[@andreaskarz]

I agree

[@neemapranay23]

In India today (5th September) we are celebrating Teachers day. And for me, you are one of the best teachers I came across. Happy Teachers Day Tim!!

[@IAmTimCorey]

Thank you!

[@robertmerritt3284]

I have no idea how anyone could possibly give this video a thumbs down. Thanks Tim! You are awesome. I'll be heading over to Patreon real soon. Appreciate all you do to make our lives easier and wealthier!

[@IAmTimCorey]

I appreciate the kind words.

[@ferrad1]

Best free C# tutorial videos online ! Thank you Sir ! Keep up the good work !

[@IAmTimCorey]

Thank you for the kind words.

[@mbvisiombvisio1170]

Very helpful video. Generics explain in a practical way. Good teaching methodology. Not overcomplicated way of sharing your knowledge. Keep it simple Tim!

[@IAmTimCorey]

I am glad it was helpful.

[@alikinng8653]

This is excellent and simple tutorial on C# generics. Thank you for your efforts and sharing your precious knowledge.Thank you sir!!

[@IAmTimCorey]

You are most welcome. Thanks for watching.

[@khaledbudajaja6137]

I have been using generics for a quite long time, but never managed to understand how to make one. you explained it very well. Many thanks Tim Corey

[@IAmTimCorey]

Awesome! I'm glad I could add to your knowledge.

[@madhavmehendale7324]

This opened my mind to a lot of things that Ive seen on your other videos but which I did not fully appreciate - until now

[@IAmTimCorey]

Excellent!

[@RahulSharma-ps1rf]

Very good teaching, the best part is that first you explain what most of us do and show the best thing. Learnt a lot

[@IAmTimCorey]

Glad to hear that

[@georgetuccio6053]

Very clever example and code Tim. Just the right amount of complexity. Liked the reflection thrown in too. Thank you.

[@IAmTimCorey]

You are welcome.

[@adityarane2758]

Best Video in Advance Topics Playlist up till now. I loved the generic methods because I faced this problem in my previous organization.

[@IAmTimCorey]

Glad it was helpful!

[@thethomasproject]

Tim, again, an older but very timeless video. Thanks for the clear explanation on generics!

[@IAmTimCorey]

You are welcome.

[@abidzahid2974]

That is an excellent and simple explanation. I had some confusion about Generic methods, which are cleared now. Thank you.

[@IAmTimCorey]

Glad it was helpful!

[@yuriymayyagruzglin1812]

As always - clear, concise, great. Thank you Tim!

[@IAmTimCorey]

You are welcome.

[@joystanrolan495]

Adicted to IAmTimCorey channel. Learning makes easy when we find the right person who can answer our questions without asking them. You are a Great teacher and your efforts are really amazing. Thank you so much Sir. Love from India

[@tomthelestaff-iamtimcorey7597]

Thanks for trusting Tim with your time.

[@charalampost769]

Thank you for your videos, there are amazing. You help me so much to learn, and your sound and spelling is so clear to make it easy to understand for people that english isnt their native language.

[@IAmTimCorey]

I am glad my content has been so helpful.

[@Redpill99]

Thanks Tim for giving so much to the community.

[@IAmTimCorey]

You are welcome.

[@testthisfordecficiencies]

Great work Tim! Your syllable timing is perfect and I can run your video at 1.25 or 1.5 times and it still seems normal to my fast Brain.

[@IAmTimCorey]

Great to hear!

[@SuperLadly]

Good one. Restriction and mentioning empty constructor was new to me. Thank you

[@IAmTimCorey]

Thank you!

[@DepressionAlgorithm]

Nice video as always Tim. Just a note on 35:20 for anyone interested in reflection: You can still grab the properties of a class, using reflection, without creating an instance of that class. This will compile and perform the same task: *var cols = typeof(T).GetProperties();* The instance was still needed in Tim's example though, since he's returning instances of that class in the Load method.

[@IAmTimCorey]

Yep, thanks for pointing that out.

[@RootofEvilify]

Thank you Tim! I work at company where we use C# and MVVM pattern, I learned some new things from you. :)

[@IAmTimCorey]

Excellent!

[@email195]

Thanks again Tim for a great tutorial. I actually just used what I learned on a project where I have a method that calls a Web API and was returning JSON. Then I would deserialize it in the calling method into the proper type. Now I just use generics and this method returns the object that I called for. So much nicer. Old code... public static async Task SendRequest(HttpMethod method, string requestUri, object payload = null) which returned the raw JSON string New code. public static async Task SendRequest(HttpMethod method, string requestUri, object payload = null) where T : class which returns JsonConvert.DeserializeObject(responsePayload)

[@IAmTimCorey]

Great! I am glad it was so useful.

[@linux_master_race]

I've been working with .NET, and primarily C#, since before it was even publicly available and I still learn great things from your videos. Thank you!

[@IAmTimCorey]

You are most welcome. Thanks for watching.

[@juliusv2073]

Some people are born to teach, you one of them. Big thanks

[@IAmTimCorey]

Thank you!

[@andrijapavlovic6322]

Best tutorials on C#! Keep going!

[@IAmTimCorey]

Awesome! Will do.

[@torrvic1156]

Merci bien for your hard efforts to enlighten us Tim! You are an inspiration to start making a good code.

[@IAmTimCorey]

You are welcome.

[@scottk5083]

That you very much. Has really improved my understanding regarding this topic. You are an excellet teacher

[@IAmTimCorey]

Awesome! I'm glad you were able to increase your understanding of the topic.

[@pioneer7161]

the beauty of this channel is it shows the practical usage of the theoretical concept.

[@IAmTimCorey]

Thanks!

[@jasper5016]

You are the greatest instructor I have ever seen. You are just awesome.

[@IAmTimCorey]

I appreciate the kind words.

[@shuvbhowmickbestin]

Wonderful content Tim. Kudos to you!

[@IAmTimCorey]

Thank you!

[@madChileRiver]

Another great video clearly explaining an area that is often misunderstood!

[@IAmTimCorey]

Thank you!

[@patatas.m1317]

You are so good sir, you explain it clearly. Even the topic is pretty advance for me, I can imagine things by your words. Thanks for making this video:)

[@IAmTimCorey]

You are welcome.

[@surajnarwate7536]

Tim , you are fabulous trainer. Keep it up. I learnt, much more from your video.

[@IAmTimCorey]

Thank you!

[@Stone8age]

This is great. You concisely explained a concept that i originally perceived to be intimidating and confusing. Bravo

[@IAmTimCorey]

I am glad it was helpful.

[@Linkario86]

Finaly an example where this is actualy useful. Now I understand the whole thing much better. Thanks a lot!

[@IAmTimCorey]

You are welcome.

[@luih7314]

You're my hero Timmy Such an emotional video, you killed off Sue Storm :)

[@IAmTimCorey]

It was a rough one, but don't forget, Sue is a comic book character. They never really die.

[@ahmer9800]

very glad i found this video. i've been trying to sort out template interfaces for days!!!

[@IAmTimCorey]

I'm glad you got value out of this video.

[@mirogeorgiev7095]

It was very helpful for me. Thank you Tim.

[@IAmTimCorey]

Glad it was helpful!

[@jean-marcblanchet2270]

Well, thank you Tim for the great content you provide for free to us, the C# developers community. I have an old habit I took when learning C language, a long time ago when I was a student. I always put my checking code at the beginning of my methods, before any declaration or usage of variables and objects. So that I get rid of incorrect or incomplete values before going further, for instance by raising an exception or returning an error code. I don't know if it's a good practice, but I'm sure data is correct after that checking step.

[@tomthelestaff-iamtimcorey7597]

Interesting, thanks for sharing that approach.

[@VinuP2023]

I appreciate all your efforts Sir. Thank you :)

[@IAmTimCorey]

You are welcome.

[@rosahartanto8055]

thanks tim corey for the sharing, hopelly continue share for next videos

[@tomthelestaff-iamtimcorey7597]

We appreciate you making Tim a part of your development journey

Thanks Tim, this video help me a lot to understand more about Generics!

[@IAmTimCorey]

I'm glad it helped you out.

[@harag9]

Great tutorial, thanks very much for your efforts on these - especially when it's 12:48 AM.. wow dedicated!

[@IAmTimCorey]

Thanks! That's actually a pretty common time for me to be recording. I only get a few hours a day where I can record right now (from about 10pm to 2am). I am actually working on some soundproofing and other things so that I can record earlier in the day without degrading the sound quality. Once I get that in place, I can record starting at about 9pm. Once I quit my day job (that is based upon the amount of income I bring in from videos), I can record all day long. That will GREATLY increase the amount of content I can put out. That is also when I'll start being able to put out a video per week in other languages that complement C# like SQL, HTML, CSS, JavaScript, etc. My first priority will be C# but once I have more time, I can support developers more fully in the other areas as well.

[@bmrreddy2002]

Tim ,If that's the route you wanna go, I honestly think you need to put out a lot of your content on Udemy and other sites and make them paid courses. Your explanation is just fantastic and you deserve to get paid for it!

[@IAmTimCorey]

Well, I will be doing more paid courses in the near future (and long-term). I have a few at IAmTimCorey.com but I'll be adding a few more soon. I've looked at Udemy but they really take a lot from teachers (50% plus they set pricing so your $40 course might be sold for $10 without your say). I really don't want to go down that road. I'll stick with my own platform where I can charge a reasonable amount and get about 95% of the asking price. I appreciate the kind words.

[@bmrreddy2002]

IAmTimCorey ah true! See I don't know what their cut is, but yes that's a lot. But you're a real good teacher and would do great doing this full time! Will take some time to get there for sure. Good luck ! :)

[@MrGegere]

Heh, I needed 6 minutes of Your video to understand what I need. Truly great content.

[@IAmTimCorey]

Thanks!

[@JohannJimenez]

Perfect explanation. Thanks.

[@IAmTimCorey]

I'm glad.

[@alexanderspiegel6747]

Here is my “like”, Tim. Thanks for the great lesson.

[@IAmTimCorey]

You are most welcome. Thanks for watching.

[@kevinrambo]

Good job! I appreciate you posting your videos.

[@IAmTimCorey]

Thanks!

[@somethingnotspecified]

This was a very helpful tutorial. Thank you!

[@IAmTimCorey]

You are welcome.

[@ViktorTy]

Hey Tim! I am a very big fan of your videos! Thank you for helping me learn C#! I was wondering if you plan to make a follow-up on generics and speak about how we can use generics and dependency inversion together as principles to make dynamic interfaces that we can reuse? I think it is a very interesting and challenging topic that most people would appreciate.

[@IAmTimCorey]

Added to the list, thanks.

[@dragonburger5676]

She glad I found this channel!! Thank you Tim!

[@tomthelestaff-iamtimcorey7597]

We are pleased you did also.

[@prubenheeren707]

Your videos are insanely good. Love it.

[@IAmTimCorey]

Thank you!

[@nelsonluisfreire8969]

Great video, and correct pace

[@IAmTimCorey]

Thanks!

[@PabloSanDev]

Great material, bravo Tim!

[@IAmTimCorey]

Thank you!

[@MrMakgotla]

wish you could go around the world to teach the teachers how to teach... wow, I feel super happy to have came across your channel. "ke a leboga, thata"(Thank you very much(all the way from RSA))

[@IAmTimCorey]

You are welcome.

[@jasonjames1849]

Excellent video, Generics have always been a bit confusing to me and it helps me best when there is a practical demo like in this video. So thanks for that

[@IAmTimCorey]

You are welcome.

[@willamsreis9715]

Great lesson, Tim. You've done a great jog teaching us how to handle with C# technology, Thank you so much.

[@IAmTimCorey]

You are welcome.

[@GabrielBauermann]

Awesome! What a great lesson. Thank you.

[@IAmTimCorey]

You are welcome.

[@chukwumaesoga5171]

I have always struggled to understand generics and how to use collections and this video just broke it down for me in the simplest way. You are awesome at how you approach topics and i jsut subscribed to you channel so i can learn more

[@IAmTimCorey]

Glad it was helpful! Thanks for the sub!

[@krishan3515]

Thank you. Very informative. Very well explained.

[@IAmTimCorey]

You are welcome.

[@gilhooli6685]

Thank you very much. I love this channel and found it very useful. I also love your way of teaching.

[@IAmTimCorey]

You are most welcome.

[@nooraldeenali4628]

It's really helpful. Sir, only with your video did I learn why, I have to use generic. Thanks a lot.

[@IAmTimCorey]

Great!

[@jeremybourgne7394]

Thanks a lot, great example! You've got to love it!

[@IAmTimCorey]

Glad you like it!

[@godfathermikal]

This is my 2nd favorite video you've made. :-)

[@IAmTimCorey]

Awesome! What's the first?

[@kimvanasselberg9659]

Now I love generics. Thanks for the great tutorial.

[@IAmTimCorey]

Excellent!

[@ademineshat]

I was busy watching your other Videos, but today was the Time, yay. I've been using a separate class like processor for every model like you said :) where i was doing queries with Dapper and Today was the day when I put them all in one place. I was allways feeling that I'm repeating my self, and I really was! Thank you very much Tim

[@IAmTimCorey]

I'm glad you were able to figure that out and improve. Well done.

[@ademineshat]

But still a Tutorial with Generics and Dapper will be great :)

[@aaronvaughan2401]

Very helpful, using reflection in the code is interesting.

[@IAmTimCorey]

Glad it was helpful!

[@movsar42]

You are that perfect c# book I was looking for!

[@IAmTimCorey]

Great!

[@VinuP2023]

Tim, 12,114 views and 418 likes and "0" dislikes as on date, That speaks quality of this video. :)

[@IAmTimCorey]

Thank you.

[@marceloleoncaceres6826]

Great example, very useful. Thanks a lot

[@IAmTimCorey]

You are welcome.

[@pcintra1]

Thanks for the great lesson Tim!

[@IAmTimCorey]

My pleasure!

[@nafisiancastle]

I learned generics before. But today I learned why and when I should use it. Thank you !

[@IAmTimCorey]

You are welcome.

[@gustavoramia]

Great video. You really know how to explain things

[@IAmTimCorey]

Thank you.

[@al-omdaahmed3191]

you are a great tutor , thank you again and again for these videos

[@IAmTimCorey]

You are welcome.

[@raguramanmanokaran1824]

Simple and Superb !!

[@IAmTimCorey]

Thank you! Cheers!

[@azizbekibnhamid642]

Great job!

[@IAmTimCorey]

Thanks!

[@longuinni]

Really nice. You make C# much easier to understand.

[@IAmTimCorey]

That's the goal. I'm glad it is working.

[@longuinni]

IAmTimCorey yes, it's working. It will be great if you make a mvvm series. I don't know why I can learn mvvm.

[@IAmTimCorey]

I do have an add-on course to my C# Application from Start to Finish course where I replace the WinForm UI with WPF (using Caliburn Micro and MVVM) if you want to check that out: iamtimcorey.com/courses/tournament-tracker-wpf-user-interface/

[@longuinni]

I don't know why I didn't see this course before! Thank you Tim!

[@fsoria]

this is the best tuts, very clear

[@IAmTimCorey]

I am glad my content is helpful to you.

[@aaronvaughan2401]

Very helpful, thank you.

[@IAmTimCorey]

You are welcome.

[@francogiulianopertile279]

Great explanation, greetings from Argentina

[@IAmTimCorey]

Thank you!

[@zulhishamtan4308]

Yes, Generic is useful, it can reduce duplicate code. Thank you very much. Very precise explanation.

[@IAmTimCorey]

You are welcome!

[@NOCKSCITNEY]

Hi Tim. Recently found you and even being an established coder, I feel I've learnt lots from you over the last week. Quick question. I too have used Generics for SQL connectivity to scale down a helper class I had for creating and reading parameter in SQL queries, going from a method for each type to generic methods to encompass all of them. Thinking about your discussion in this video about doing it also for the SQL connectivity portion, would Generics work for a "void" method declaration as well as where a return type is needed? My thought on this without experimenting of course, is that you'd have 2 methods, one where there is a return type and then another where there isn't? Would that be the case?

[@RockmanR]

Your videos are clear and simple and I enjoy watching it. I've tried Pluralsight before and all of the teachers so far (like 4 people) were unnecessarily complicating stuff and were very formal and boring. Thanks a million Tim.

[@IAmTimCorey]

I appreciate the kind words.

[@gleisonsubzeroKZ]

thanks a lot for this excellent and wonderful tutorial about generics. I made some changes on reflection parts and I would share with you guys: public static List LoadFromTextFile(string filePath) where T : class, new() { var lines = System.IO.File.ReadAllLines(filePath).ToList(); List outputList = new List(); var properties = typeof(T).GetProperties(); if (lines.Count < 2) throw new IndexOutOfRangeException("The file was either empty or missing."); // Splits the header into one column header per entry var headerColumns = lines[0].Split(','); lines.RemoveAt(0); foreach (var row in lines) { T entry = new T(); var rowValues = row.Split(','); foreach (var column in headerColumns.Select((columnName, columnIndex) => new { columnName, columnIndex })) { var propertyRef = properties.SingleOrDefault(property => property.Name == column.columnName); if (propertyRef != null) { object typedValue = Convert.ChangeType(rowValues[column.columnIndex], propertyRef.PropertyType); propertyRef.SetValue(entry, typedValue); } } outputList.Add(entry); } return outputList; } public static void SaveToTextFile(List lstData, string filePath) where T : class { List lines = new List(); if (!(lstData?.Count > 0)) throw new ArgumentNullException("data", "You must populate the data parameter with at least one value."); var properties = typeof(T).GetProperties(); lines.Add(string.Join(",", properties.Select(c => c.Name))); foreach (var row in lstData) { var rowValues = properties.Select(c => c.GetValue(row)).ToList(); lines.Add(string.Join(",", rowValues)); } System.IO.File.WriteAllLines(filePath, lines); }

[@IAmTimCorey]

Thanks for sharing.

[@mindawakening3873]

Absolutely awesome!

[@IAmTimCorey]

Thanks!

[@jayjayjaythebrand]

Everyone on here has benefitted from Tim in one way or another. Please subscribe to this man's Patreon, even if it's just the $1, that's nothing compared to the value he provides us for FREE! Support this guy!!!

[@IAmTimCorey]

I appreciate the kind words and the support.

[@StreetBladerBloke]

Or sign up his courses to support him..

[@mohammadjavadtavakoli7977]

Thank you Tim!

[@IAmTimCorey]

You are welcome.

[@betozurita151]

Great Tutorial. Thanks!

[@IAmTimCorey]

You are welcome.

[@dansolarta8937]

am impressed, i wanna do more generics with different class properties.

[@IAmTimCorey]

Great!