Equality in Dart | Decoding Flutter 

This is correct, overriding equality with hash code only can result in some very very serious bugs, especially data corruption. Please get this video reviewed by any SDE at Google and everyone will tell you the same thing, that this breaks the equality contract and is very bad. This video should be pulled for spouting this dangerous misinformation. Otherwise it would have been a great video.

@@fitness7065 Edited second part below: This is not overriding anything in the way equality works, it's just overriding the hash code for a Class that extends the Equatable package/class. So normal equality will be just fine and won't be broken. I previously stated that Dart uses the hashCode to compare equality of objects but that was incorrect. In the end, it natively uses the pointer address to compare two objects. Also, @Julien Scholz's edited statement that the Equatable package does not use the hashCode to do a equality check is correct. It does update the hashCode to be the same between two instances of the same class that have the same values however, so hash tables and the like would consider the object already existing if a second instance is added that has the same values. Finally, while it is possible that there would be collisions, doing a comparison with the hashCode as demonstrated in the video wouldn't be as catastrophic as is being suggested. The first check is that the two objects are of the same type. So for a collision to happen, you would have to have two objects of the same type that have values that then collide, which is a pretty unlikely situation in the real world.

@@Aragorn450 Hi Charlie, thanks for the reply! I'm referring to the override described at 3:37 in the video, and the explanation that begins a few seconds before that. That appears to be overriding the default equality and breaking the equality contract.

Hey all, thanks for the feedback! I didn't intend for that to be stopping point; merely a building block toward understanding what Equatable does and why you'd want to use it. I'll be more careful with phrasing around intermediate steps in the future.

We always love hearing feedback from viewers like you! Glad to hear you enjoyed it. Thanks for the love 🙌

You've made a great point, Rudolf 🎯 Let us know how you'll be using this feature for your project or app!

When using flutter_bloc it's a must have. It ensure that your state is well emitted and not removed because object seem the same.

You may use it in your unit tests. For example, if you wanna test if two instances of an object are equivalent, you can use the expect function of package test. It will use the equal operator, and by overriding the equal operator, we can verify if they are the "same" or not.

To be clear, it's not exactly overriding the operator, it's just overriding how Flutter gets the value of the specific class you've defined that has that override enabled. For instance, doing something like this wouldn't allow you to make 3 == 4 return true. But you COULD make A(1) == A(2) return true with this...

Thanks a lot for all the tips! I can't help falling in love with Flutter.

So what alternative do u use? Or you haven’t had an encounter with equalities?

Yes, hash collisions should always mean that two objects are "the same". The idea here is that you get to define what "the same" means!

@@laybunzz Thanks for all the great work, but substituting component wise comparison of fields in the equals operator with a single comparison of hash codes breaks the contract of the equals operator. Two objects that are equal must have the same hash code, but two objects which are not equal are allowed to have the same hash code, too.

@@gabrielterwesten3262 I don't think such substitution actually breaks the contract. Two equal objects (according to our new definition of equal) will always have the same hashcode. Non equal objects will never have the same hashcode, but that's not part of the contract. :) It can still be wrong though, since two objects that would not be equal by standard definition (comparing each field individually) might be accidentally detected as equal due to hash collisions.

@@dongdigital The contract of the equality operator and the hashCode getter as specified in the API docs are not really optional. Collections rely on the correct implementation of those contracts. The type of equality specified there cannot be implemented with hash codes because of the collisions.

We're glad you found Craig's tutorial helpful, Alexandru! To help you on your Flutter journey, feel free to check out more Decoding Flutter episodes → goo.gle/DecodingFlutter Happy Fluttering 😁

@@flutterdev I will thx!

We couldn't agree more, Pedro! We have even more resources for our Flutter community. Try your hand at one of our amazing codelabs, and the best part? You can follow along at your own pace 🙌: goo.gle/flutter-codelabs

Thanks so much! As for the animations, we have a really talented team that uses After Effects to bring these videos to life :)

Future is used because it provides a Boolean value in the future. Suppose you've to get data from some task but that task will take a few seconds or minutes to complete but it may block the main thread if we will wait for it. So to make the task asynchronous, we use await keyword and that's where Future value comes in. The task will complete asynchronously and then you'll get the value. You can further change the state of the widget to make changes in the screen using that awaited value. Hope this helps. :-)

@@prankcial4187 Bro thanks for replying, but my question is, when you get the asynchronous bool result it can't be used anywhere. The major use case of bool variable is to check whether the condition is true or false. Suppose I have written a function to check whether the device is connected to the internet or not, and it will ping to my server, and on successful connection it will return Future (true) on any socket exception (false). But the real problem is, you can't use the Future anywhere, neither in if else statement, nor you can assign it to other local bool variables. If you try to do so, the error will be: 'Future ' is not a subtype of type bool The internet checking example I mentioned was not a big issue, you can anyhow solve that by assigning the value to a global bool variable. But in some scenarios it will become really difficult to overcome this issue

Yes it does, with the help of the collections package, it checks if the properties in the props is a map, iterable or list and compares it with DeepCollectionEquality

You have equatable mixin for that case.

Use equatable mixin. Avoid writing boilerplate code

​ @Yayo Arellano ​ @sahil kumar oh cool. It's been long I used the package. I didn't know about that. But I think i'll stick to the vs code extension. Rather than importing another dependency, It's easier and better in my opinion to use the extension to generate the code for me. "cmd + ." is all I need.

Well it's really not, basically you should mostly compare the properties inside your logic rather then the class itself

No answer 😭

@@abdullahaqrabawy6897 you could use microsoft powerpoint or other presentation software that support fade in

@@abdullahaqrabawy6897 We use After Effects!

Still topping😁

Getting started is tricky sometimes, we do offer many resources to help you get started however! Check out our Begin learning Flutter series right here on RU-vid: goo.gle/3CL1VlD If you prefer written guides, we also have a Get started guide on our resource site: goo.gle/3SRCSDe We can't wait to see what you create 🙌 🌠

@@flutterdev Thanks so much for this 🤗

Sorry for being blunt. I like dart, and i hope you can improve this feature in the future

Why? Seems like many other languages, objects have their references compared unless you override the equality operator. What is a mess in this?

@@dancovich First thing: There is only the == operator left for equality, so how do you differentiate equality and identity like Java does with equals() and ==? Second thing: To make equality manageable they offer a library and you have to extend Equatable - this really is so '90s.

​@@marcom. Dart has the `identical` function, part of the SDK, which will always compare references. Dart approach is that == will aways run whatever routine is writen for the operator and "identical" will always compare references. The reason == compares references by default is because the Object class uses "identical" in its == operator, so every class inherits this behavior by default. So, both Java and Dart have two ways of comparing, one is overridable and one is not. Only difference is that in Dart what is overridable is the behavior of the operator while Java what is overridable is the method. This isn't more or less confusing, it's just a different approach for the same issue that these languages don't have any operator for saying you're copying the value of an object to another and not just copying the reference.

​@@marcom. I understand your point, but you don't need to use equatable if you don't want to. I personally used it in the past, but nowadays, I prefer using a VS Code extension called Dart Data Class Generator to override the == operator and hashCode. I want my entities to be apart of any external dependencies, even if its a great package like equatable or dartz, for example. Dart is not a mess like other languages. Dart gives you the basics of a programming language, and by doing so, it can be really predictable and safe to use.

For example, Dart don't have interfaces. Instead, you should use abstract classes. Dart don't support method overloading, which is SUPER common in Java, but instead, you should use factories to "overload" constructors and create another function to "overload" a method. In my humble opinion, this is much better. Methods and constructors have meaningful names, and this is great in terms of readability.

You're truly welcome, Rohith. We're loving this cool package as well 🧊