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‫All right.

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‫So now that, you know, the general idea of delegates, let's look at them in action.

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‫And to understand them better, we will start by using a delegate that already exists in C-sharp.

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‫So, first of all, let's start by defining a simple list of strings called names.

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‫And then I'm going to use this.

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‫Let's say I want to remove names from it.

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‫So here there is this remove all method and this remove all method allows me to remove all the elements

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‫that match the conditions defined by the specified predicate.

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‫So here you see this green predicate keyword.

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‫Here is basically what we can pass.

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‫So this is basically here I delegates that is expected predicate is just the name of the delegate that

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‫is expected.

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‫Once you click on it, you will find it here.

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‫Public delegate pool predicate.

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‫So here we can see that the predicate is a delegate that takes an object of RT, which means specific

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‫type.

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‫In this case, RT is the type of our list elements.

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‫So in our case it's a string and it returns a boolean.

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‫So when we call the remove all method, this predicate will be called on every name in our list.

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‫If we read the documentation, we will learn that the bool that is returned by this predicate will determine

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‫whether or not this element will be removed from the list.

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‫If it returns true, then the element will be removed.

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‫And it is our job to write these rules to determine the fate of our names in our list.

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‫So of these names that we have here, which means Aidan's if folder and Anatoly.

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‫After all, the people who wrote the code behind the remove all method can't read our minds to determine

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‫the rules we want.

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‫Exactly.

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‫That's why we will create our own method that matches the definition of the predicate delegate and pass

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‫it to the remove all method.

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‫Let's say we want to remove all the names that contain the letter I so we can write our filtration method

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‫like so.

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‫So we just create a static pool filter which will take in a string.

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‫So this is our method called filter, and we return whether the string contains the letter I.

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‫And here we're using the contains method which will return a boolean which will return true or false.

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‫So here the contains the C, it takes a string checks if it contains that, and then it returns a boolean.

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‫So what we do here is we in fact return a boolean.

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‫And it takes a string as a parameter.

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‫So basically we will return.

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‫True if the string contains I and then the remove all method will execute this filter method on all

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‫the elements in our list.

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‫So let's now pass our filter method to the remove all method that we have up here that isn't finished

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‫yet and still needs a delegate that we can pass to it.

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‫And let's add a for each loop before and after the remove all method just for observation.

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‫So I'm going to add this little code in here where I just say this is what happened before.

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‫So we write a list of names onto the console with all the names that are in our list here.

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‫And then we remove all that, follow a certain filter, and we run it once again.

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‫Now this filter that we're passing, you see, we don't use the brackets here, even though it's a method.

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‫So basically we're passing a method as a parameter here and we're checking if the string that we're

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‫passing contains an AI.

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‫So let's run it and see which names contain an I.

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‫So we have agents if Walter and Anatoly.

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‫And after that, we removed all except for Walter, because Walter is a string that doesn't contain

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‫an eye.

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‫And that's basically how we have used a delegate that was pre-existing.

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‫And now we have used a method that requires a delegate that we can pass to it.

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‫So basically what happened is that names this list of strings here.

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‫Was given to remove all and checked one by one with the filter that we have used here.

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‫So it passed every single value from names one after the other into our filter method, ran through

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‫that filter and returned if it should delete it or not.

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‫So this boolean will be true if I is contained in the string that was passed.

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‫So the string that we're currently looking at in our names list and if this here returns true, then

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‫the filter method will return true, which will then lead to remove all taking care of removing the

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‫name from the names list.

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‫All right, so this was just one example of a delegate.

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‫And you see, we didn't pass specifically here what we want to have.

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‫So we didn't say which string we want to take, for example, by saying name starts and then index or

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‫whatever.

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‫We didn't have to do any of that because well remove all expects a delegate here and that's what we

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‫passed to it.

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‫If this is still a little confusing, no worries.

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‫We're going to have a couple more examples which will definitely help you to understand delegates a

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‫little better, because we're going to create some ourselves and then it will make a lot more sense.

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‫So see you in the next video.