Thanks for the above one. Double dispatch couldn't be simplified more.Can you t explain examples of Extension object and Template method design pattern:)
I wonder all over the internet to find the best to learn visitor design pattern and finally landed here and writing comments middle of the video, This is an awesome video so far I came across. Buddy keep it up you are the best.. !!!!
2:50 UML dia of Visitor Pattern 4:20 the original piece of hierarchy 6:50 why - single vs double dispatch 7:39 single dispatch 8:14 what single dispatch allows us to do 9:58 double dispatch: interaction of 2 objects 10:12 example 10:28 modify the interface: in Animal interface, add makeSound(Dog) and makeSound(Cat) 11:45 *compile error* due to not support on double dispatch
I've seen lot of videos on this pattern but this is most real life understanding video on Visitor pattern, Thanks for this amazing video... luckily found this
This was amazing! A colleague of mine used this pattern without using "visitor" in the name. I understood the structure and how to use his design, but I didn't fully grasp everything that was going on or how he even came up with it. He mentioned visitor and here I am. Thanks for the concise but real world example.
i'm no kidding there's a job offer in play here, and I have to deliver a code using this very pattern and i couldn't get it before watching this amazing explanation of yours! thank you for time and help from Brazil!
I would love to see constructive criticism from someone who disliked this video. I think it's unbelievably helpful, especially given that you explained the whole "dispatch" thing, which is not obvious at all for beginners. Thank you very much!
I'm so grateful for it, good job! I always struggle with theoretical explanations and definitions, so combining them with actual examples made it so much easier to understand.
Awesome explanation and helpful example! I hadn't realize before about the double dispatch problem. I really liked that you didn't over-explain things keeping it short and to the point. Also thumbs up for cutting out the tedious parts where you just paste code. Thank you!
Awesommest post on the internet on Visitor Design Pattern !! Understood everything in such a simple way that its gonna stuck in my mind forever !! Subscribed !! Thank you..may you have many more "Visitors" on your channel 😅🤟!
Excellent explanation especially of the why. A lot of tutorials just go straight into the how. I think given the extensibility problem, I might have initially gone down the passing of delegate route or maybe another interface - but I guess this seems somewhat tidier. Note to any other C# Developers reading before watching, the video is still easy to follow. Well Done 👍🏾
Amazing explanation. I like discussions a lot when it cover the background as well like why something is needed, current limitations in some paradigm and ways to solve that. Thanks a lot for the video. :)
Very nice videos probably the best on the internet. Please do other patterns as well with the same kind of explanations you have done in these videos. Thanks.
Isn't this still tightly coupled though? If you get rid of the Bronze Card or add a Platinum card, you have to update your OfferVisitor interface and all of the classes that implement OfferVisitor right? That's still a maintenance nightmare. It seems like the problem wasn't solved but just relocated.
Simply excellent explanation of this design pattern. As you said, this one is underestimated but it is super useful. Please consider doing some other design patterns, especially the "not easy" ones Thanks again for this video
Great explanation, thanks! My question is the following: we made CreditCard easy to extend without needing to modify it, but now OfferVisitor kinda is in the situation we wanted to avoid, right? If we create a new PlatinumCreditCard, the OfferVisitor will have to define visitPlatinumCreditCard, and all the visitors will have to implement it. It feels like we need to take a guess at which side (credit card or offer) is more likely to be extended in the future, and use a visitor pattern for that one. But we can’t have that for both of them. Is that right?
I think the idea is you might add a card once or twice a year but maybe 3 or 4 offers a month. I guess what we would normally to is have a GetCashBack(CreditCard, Offer) method but then there would be the overhead of maintaining a datastore
I think so like the a scenario like the one described on this video. You don't come up with new credits cards every day, but you may get new offers every day/month.
This is a great video. Super clear explanation, great example, and the whole video was really well done. Thanks so much for your work, it's really helped me understand the pattern and I am now going to go check out your channel for more content, which I'm sure will be as good :) thumbs up!
This is really fantastic. Is it possible to combine this pattern with the Factory pattern for example to dynamically determing which credit card to use in a certain scenario
Thank you for good explanation. Your final implementation require small correction. Visitors classes should have overloaded method rather than different name for different CreditCard. Otherwise it will work without double dispatch.
Hi Ryan - so could you please tell how I apply Visit/Accept pattern to resolve the original problem of cat-bark or dog-meow you originally started with ? Should I create one more class like CATDOG from Animal, accept runner request and forward to makeSound Visitor - visit(CATDOG). Or simply type-check a => in Dog "makeSound(Animal a)" for Runner request of "dog.makeSound(cat)" and take action . Much appreciate and thanx.
One small question - The GasOfferVisitor has 3 methods for the 3 types of credit cards. What if GasOffer is not applicable to Bronze Credit card? So in the GasOfferVisitor class you may remove that method pertaining to Bronze OR throw an exception from there? Whereas from the main method, BronzeCard would still be okay to accept GasOfferVisitor object as an input param at compile to only get a runtime exception or empty response. How can this use case be handled?
The way I see it visitor pattern doesn't make you write any less code but it gives the advantage of decoupling. But even so, it kind of does and then it doesn't. In the "multi-dimensional" case like cards/offers it all depends on which of the dimensions you're likely to have more classes added. Even if card types are issued occasionally, for every new card you have to make modifications in every _offerVisitor_ . And there may be an order of magnitude more _offerVisitor_ classes than cards because that's precisely the case that visitor pattern tries to mitigate - many offers, few cards.
@@lascau2918 Not only O but I as well. Think about the case where a credit card only has certain offers or there's an offer that only applies to certain credit cards (it depends on how you look at it). The key is not enforcing all combinations, i.e. not enforce implementation of all those interface methods. I'm thinking we could modify the visitor part a bit. Abstract out individual card-offer combination into something like _Interaction_ that would have an _interact()_ method that does the calculation . _OfferVisitor_ would have a _List_ . I haven't thought this through but the idea behind this more complicated structure is: 1. Each new card doesn't imply modifying all offers. 2. Only have implementations for actual card-offer combinations, and not also for nonexistent combinations.
it would be a hit if you could do a series or video that puts together and deploys a multi platform mobile app. bonus if it has animation , audio and 3d capability.
Can we say one drawback of this pattern is that the visitor needs to have a visit method for all card types even if it might not apply to that card? Is there a way to overcome this necessity?
This was the best resource I've found so far, but unsurprisingly, I am a bit confused. First: I guess we need to write a new `accept` method for each type of resource (e.g. offer) that Element can take (in this case, Bronze, SIlver, Gold credit cards.) We are not able to share `accept` methods between concepts: e.g. Not just offers (hotel, gas), but also other behaviour, like update state, get description, expiry. Could someone suggest a better name for accept? Second: The video author also wrote 'visitBronzeCreditCard' instead of just 'visit', so this actually goes around the problem of (not highlighting how visitor patterns overcomes lack of double dispatch)
Is the problem presented in Single vs Double Dispatch actually correct? When you implement a makeSound that receives a parameter that is an AbstractClass, you don't actually know which object received it, but you know which one is calling makeSound, (e.g. you implement makeSound on dog that receives Animal, you know that the makeSound that is called is the makeSound of Dog, therefore Dog interacts with Animal, and not the other way around).
If you later have a need for a different type of visitor, such as Discounts, how do you alter the pattern to handle this? Do you override accept() for each visitor type (requiring an alteration to each credit card) or do you create a generic Visitor implementation for any visitor type that may arise?
I guess only the name of 'OfferVisitor' is a little misleading. In my opinion naming it like 'CreditCardVisitor' would make it clearer as it is visiting the Creditcard structure and 'reacts' accodingly to the CreditCard implementations. By then you could potentially implement any logic as a visitor and throw it at the CreditCard object graph.
If one more card type is introduced, then offervisitor interface need to be updated with one new function which support new card type right?? Is this violate solid design principle??
yes, you need to implement new method. But only ones. But your can add new visititors with new card withour changing new methods. So, yeah, it's kinda violite solid principle in a some way, that's why Common Lisp is definetly better in this current situation. But if we use java/c++ we should accept this drawback, nothing we can do, basically. (Not talking about c++23 code generation possibilities)
GoldCreditCard silver Had no effect on the running code, but boy did it trip my OCD! lulz :P I think it would have done better to drill into why you couldn't pass cat to itself. Basically, you can't pass ancestors references into descendant params and vars. The compiler gives you that hairy eyeball because the running app can't use a crystal ball to figure out which descendant you meant. I think it was part of your higher-level explanation, but for newbs, the underlying problem wasn't as clear.
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Let me know what design patterns you want to learn!
@@dg10mcdos cool 🙂 I'll do that one next
Thanks for the above one. Double dispatch couldn't be simplified more.Can you t explain examples of Extension object and Template method design pattern:)
Can you do a decorator?
Can you please make a video on strategy design pattern?
I would like to understand the Mediator design pattern if possible. Thank you for this video!!
This is probably the best video on the net for this pattern with a perfect example.Thank you!
Problem: 12:56
Solution: 28:00
Fantastic video!
Thank you! So many other videos on this feel rushed and don't go into enough detail.
I wonder all over the internet to find the best to learn visitor design pattern and finally landed here and writing comments middle of the video, This is an awesome video so far I came across. Buddy keep it up you are the best.. !!!!
2:50 UML dia of Visitor Pattern
4:20 the original piece of hierarchy
6:50 why - single vs double dispatch
7:39 single dispatch
8:14 what single dispatch allows us to do
9:58 double dispatch: interaction of 2 objects
10:12 example
10:28 modify the interface: in Animal interface, add makeSound(Dog) and makeSound(Cat)
11:45 *compile error* due to not support on double dispatch
He has made the pattern as easy to understand as hard it is going through other explanations on the web. Amazing!!
Best explanation I saw so far on RUclips!! Thank's!
I've seen lot of videos on this pattern but this is most real life understanding video on Visitor pattern, Thanks for this amazing video... luckily found this
THE only video explain this pattern in the right way ! explination, diagramme and exemple with code all are perfect
This was amazing! A colleague of mine used this pattern without using "visitor" in the name. I understood the structure and how to use his design, but I didn't fully grasp everything that was going on or how he even came up with it. He mentioned visitor and here I am. Thanks for the concise but real world example.
Great to hear!
i'm no kidding there's a job offer in play here, and I have to deliver a code using this very pattern and i couldn't get it before watching this amazing explanation of yours!
thank you for time and help from Brazil!
The best explanation anyone can find on this planet. Absolutely loved it!!
Finally make sense. Knowing what to accomplish makes it easier to understand how to do it
I would love to see constructive criticism from someone who disliked this video. I think it's unbelievably helpful, especially given that you explained the whole "dispatch" thing, which is not obvious at all for beginners. Thank you very much!
Thanks, glad you liked it!
really good video. came here to understand rsql-parser visitor pattern. I can see that this pattern explains open closed principle very well
Best content so far!!
You won't need to read anything else after watching this.
This is one of the best explanations of double dispatch I have come across!
by far much cleaner explanation. visitor is mystrio no more. thank you
This is the most clear explanation I have ever seen.
One of the best explanation of the visitor pattern
You are the best explaining design patterns. You should make a single video for every single pattern in the book. Thanks a lot for your teach.
Very good explenation, this is the Video I was searching for the whole time
I'm so grateful for it, good job! I always struggle with theoretical explanations and definitions, so combining them with actual examples made it so much easier to understand.
very clear explanation of visitor pattern with real world examples
Excelent bro... i've just spend a lot of time trying to understand this patterm. And you did it in just 30min :) thanks..
Gotta be the best explanation of the pattern I've seen yet. Thank you for making this free :)
Awesome explanation and helpful example! I hadn't realize before about the double dispatch problem.
I really liked that you didn't over-explain things keeping it short and to the point.
Also thumbs up for cutting out the tedious parts where you just paste code.
Thank you!
Just half way through the video, and I would like to say "Good Job". (y)
Awesommest post on the internet on Visitor Design Pattern !! Understood everything in such a simple way that its gonna stuck in my mind forever !! Subscribed !! Thank you..may you have many more "Visitors" on your channel 😅🤟!
Very good explanation. So far the best explanation and presentation on this pattern and finally I got it understood. Thank you very much.
Really like your video. Especially that you extend fake Animal interface use case to something more realistic.
Great content. Much cleaner than many of docs I read.
Thanks for the clear and straightforward explanation.
very well explained.it's really one of the most underrated patterns
Excellent explanation especially of the why. A lot of tutorials just go straight into the how.
I think given the extensibility problem, I might have initially gone down the passing of delegate route or maybe another interface - but I guess this seems somewhat tidier.
Note to any other C# Developers reading before watching, the video is still easy to follow.
Well Done 👍🏾
The greatest tutorial for the Visitor pattern I found so far! Thanks.
Amazing explanation. I like discussions a lot when it cover the background as well like why something is needed, current limitations in some paradigm and ways to solve that. Thanks a lot for the video. :)
Really nice explanation. I hope you would do a complete playlist of all design patterns. It is a shame that you made only 3 design patterns.
Very clear presentation and illustrative code. Thanks
Finally found a great video for visitor pattern! Hope you can make more design pattern tutorials
great job man, love your setup as well
Very nice videos probably the best on the internet. Please do other patterns as well with the same kind of explanations you have done in these videos. Thanks.
At around 13:00, we could have used instanceof and casting to get the correct Cat or Dog object though?
@the simple engineer
Great explanation, easy to memorize
Isn't this still tightly coupled though? If you get rid of the Bronze Card or add a Platinum card, you have to update your OfferVisitor interface and all of the classes that implement OfferVisitor right? That's still a maintenance nightmare. It seems like the problem wasn't solved but just relocated.
There will always be some coupling, but the amount is reduced as your class base grows large.
thank you very much, I finally understood the essence of this pattern
Simply excellent explanation of this design pattern.
As you said, this one is underestimated but it is super useful.
Please consider doing some other design patterns, especially the "not easy" ones
Thanks again for this video
The best video on the internet. Thanks for.
Beautifully explained.
loved the way you explained it with an implementation made the video so much more intuitive!!
Such a clear explanation and great examples. Thank you so much for this 😊
Super explanation of Visitor Design pattern.
Concise!, Clear!! and Simple!!! Thank You!
I genuinely loved your video and your explanation
Great great great explanation. Totally understood! Big thanks
This was very nicely explained. Thanks
Great explanation, thanks! My question is the following: we made CreditCard easy to extend without needing to modify it, but now OfferVisitor kinda is in the situation we wanted to avoid, right? If we create a new PlatinumCreditCard, the OfferVisitor will have to define visitPlatinumCreditCard, and all the visitors will have to implement it. It feels like we need to take a guess at which side (credit card or offer) is more likely to be extended in the future, and use a visitor pattern for that one. But we can’t have that for both of them. Is that right?
I think the idea is you might add a card once or twice a year but maybe 3 or 4 offers a month.
I guess what we would normally to is have a GetCashBack(CreditCard, Offer) method but then there would be the overhead of maintaining a datastore
I think so like the a scenario like the one described on this video.
You don't come up with new credits cards every day, but you may get new offers every day/month.
Very good explanation of the concept! Helped a lot!
14:07 example of double dispatch (faking) - visitor 14:23 -
17:46
18:57 the concrete visitor: GasOffer, HotelOffer ...
19:32 CreditCard interface code
20:32 OfferVisitor
23:37 GasOfferVisitor
The best Explanation !
Very clearly and neatly done. Thank you!
this is great video. I wish you would continue more on this playlist.
This is a great video. Super clear explanation, great example, and the whole video was really well done.
Thanks so much for your work, it's really helped me understand the pattern and I am now going to go check out your channel for more content, which I'm sure will be as good :) thumbs up!
Legend.. thanks for the great explanation man.
very good video, explaining single vs double dispatch really cleared it up. The only thing I didn't like was the intro
Thank you. Perfect explanation with a perfect example.
great job man, really appreciated💪👏
This is really fantastic. Is it possible to combine this pattern with the Factory pattern for example to dynamically determing which credit card to use in a certain scenario
Excellent explanation!
Very well explained. Thanks!
Thank you for good explanation. Your final implementation require small correction. Visitors classes should have overloaded method rather than different name for different CreditCard. Otherwise it will work without double dispatch.
Hi Ryan - so could you please tell how I apply Visit/Accept pattern to resolve the original problem of cat-bark or dog-meow you originally started with ? Should I create one more class like CATDOG from Animal, accept runner request and forward to makeSound Visitor - visit(CATDOG). Or simply type-check a => in Dog "makeSound(Animal a)" for Runner request of "dog.makeSound(cat)" and take action . Much appreciate and thanx.
WTF this is so well explained! Thanks, saved my finals :)
Crisp! Good job!
One small question - The GasOfferVisitor has 3 methods for the 3 types of credit cards. What if GasOffer is not applicable to Bronze Credit card? So in the GasOfferVisitor class you may remove that method pertaining to Bronze OR throw an exception from there? Whereas from the main method, BronzeCard would still be okay to accept GasOfferVisitor object as an input param at compile to only get a runtime exception or empty response. How can this use case be handled?
Thank you for doing this. Really clear explanation.
Very clear video!
The way I see it visitor pattern doesn't make you write any less code but it gives the advantage of decoupling. But even so, it kind of does and then it doesn't. In the "multi-dimensional" case like cards/offers it all depends on which of the dimensions you're likely to have more classes added.
Even if card types are issued occasionally, for every new card you have to make modifications in every _offerVisitor_ . And there may be an order of magnitude more _offerVisitor_ classes than cards because that's precisely the case that visitor pattern tries to mitigate - many offers, few cards.
@mzma You are right but what if both cards and offers increase drastically what is the solution/pattern such that you obey the O from SOLID?
@@lascau2918 Not only O but I as well. Think about the case where a credit card only has certain offers or there's an offer that only applies to certain credit cards (it depends on how you look at it).
The key is not enforcing all combinations, i.e. not enforce implementation of all those interface methods.
I'm thinking we could modify the visitor part a bit. Abstract out individual card-offer combination into something like _Interaction_ that would have an _interact()_ method that does the calculation . _OfferVisitor_ would have a _List_ .
I haven't thought this through but the idea behind this more complicated structure is:
1. Each new card doesn't imply modifying all offers.
2. Only have implementations for actual card-offer combinations, and not also for nonexistent combinations.
Beautifully explained
Thank you for the great video! can we use Async/Await with visitor Pattern since what i intend to do in visitor is make outgoing calls.
Excellent explanation. Thanks so much.
it would be a hit if you could do a series or video that puts together and deploys a multi platform mobile app. bonus if it has animation , audio and 3d capability.
Can we say one drawback of this pattern is that the visitor needs to have a visit method for all card types even if it might not apply to that card? Is there a way to overcome this necessity?
This was the best resource I've found so far, but unsurprisingly, I am a bit confused.
First: I guess we need to write a new `accept` method for each type of resource (e.g. offer) that Element can take (in this case, Bronze, SIlver, Gold credit cards.) We are not able to share `accept` methods between concepts: e.g. Not just offers (hotel, gas), but also other behaviour, like update state, get description, expiry. Could someone suggest a better name for accept?
Second: The video author also wrote 'visitBronzeCreditCard' instead of just 'visit', so this actually goes around the problem of (not highlighting how visitor patterns overcomes lack of double dispatch)
Good job on the video, heads up though the intro music could be tuned down a bit since it feels a lot louder than the rest of the audio
Is the problem presented in Single vs Double Dispatch actually correct? When you implement a makeSound that receives a parameter that is an AbstractClass, you don't actually know which object received it, but you know which one is calling makeSound, (e.g. you implement makeSound on dog that receives Animal, you know that the makeSound that is called is the makeSound of Dog, therefore Dog interacts with Animal, and not the other way around).
Amazing video! Thanks for the explanation
If you later have a need for a different type of visitor, such as Discounts, how do you alter the pattern to handle this? Do you override accept() for each visitor type (requiring an alteration to each credit card) or do you create a generic Visitor implementation for any visitor type that may arise?
I guess only the name of 'OfferVisitor' is a little misleading. In my opinion naming it like 'CreditCardVisitor' would make it clearer as it is visiting the Creditcard structure and 'reacts' accodingly to the CreditCard implementations. By then you could potentially implement any logic as a visitor and throw it at the CreditCard object graph.
Great job!
Brilliant explanation.
1:08 visitor pattern
2:48 UML
Wow. awesome video. great explanation. thank you
Wow, pretty legit!! I understand!! Thanks a lot!
Good Job Bro!!!
If one more card type is introduced, then offervisitor interface need to be updated with one new function which support new card type right?? Is this violate solid design principle??
yes, you need to implement new method. But only ones. But your can add new visititors with new card withour changing new methods.
So, yeah, it's kinda violite solid principle in a some way, that's why Common Lisp is definetly better in this current situation.
But if we use java/c++ we should accept this drawback, nothing we can do, basically. (Not talking about c++23 code generation possibilities)
Very good explanation
I don’t understand how you can access attribut of the object accepting a visitor inside the visitor function, isn’t a problem?
Thanks for the intuitive example! a larger font would be great
GoldCreditCard silver
Had no effect on the running code, but boy did it trip my OCD! lulz :P
I think it would have done better to drill into why you couldn't pass cat to itself. Basically, you can't pass ancestors references into descendant params and vars. The compiler gives you that hairy eyeball because the running app can't use a crystal ball to figure out which descendant you meant. I think it was part of your higher-level explanation, but for newbs, the underlying problem wasn't as clear.