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This lecture is going to be a bit more of just talking and not much coding as these are important concepts

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to understand.

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With that, there are three traits that we need to cover.

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We have F an F and mute and F in once.

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Effen is the family of closures and functions that you can call multiple times without restrictions,

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and it borrows values from the environment immutably.

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And this is the highest category and it includes all little F, includes all F in functions.

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F in mute is the family of closures that can be called multiple times if the closure itself is declared

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mute and immutably borrows values.

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F and once is the family of closures that can be called once.

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If the caller owns the closure and then the once part of the name is because the closure cannot take

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ownership of the same variables more than once.

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So every big fan meets the requirements for fan mute and every FM mute meets the requirements for F

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and once.

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And this means that fan is a subtree of F and mute and f and mute is a sub trait of F and wants.

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Therefore we can conclude that f an is the most exclusive and most powerful trait of the three.

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So let's take a look at three separate closures and try to establish which trait each example falls

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under.

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So the first example is going to be a closure that takes no parameters and then drops a value.

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The second one is going to take an argument and then check to see if a vector contains the argument.

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And the last one is going to also take an ARG and then it's going to push into the vector that argh!

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So take a second and try to establish which trait goes with which example.

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All right.

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So the first example is going to be F and once because we can only drop the value once.

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The second example is going to implement often because all we're doing is checking to see if the vector

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contains the parameter that was passed in.

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There is nothing required in this that needs to be mutable.

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And then lastly, this is often mute because the vector would need to be mutable in order for us to

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push the argument into the vector.

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And that's really all there is to it for the F and trait.

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So now let's talk about copying and clone enclosures.

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The rules for copying and cloning work like the regular copy and clone and rest, will automatically

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figure out which closers can implement copy and clone and which closers cannot.

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So let's take a look at two simple examples.

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So for this one, we're going to create a value by assign it five, and then we're going to create a

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closure here that's going to take an argument and then add it to our Y value.

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And now we're going to take a copy of the add y closure we created.

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So this is.

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Closure being copied.

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And now we can check to make sure that our copy actually worked correctly so we can say add y and then

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in here we can also call copy and we'll give it the value ten.

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So if this copy works correctly, we would expect 20 to be printed out because here we're designated

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that the closure is being copied.

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We are going to add 5 to 10 and then on the outer call, we're going to add five to the now value being

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passed in of 15.

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So if we run this.

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We got the expected output there of 20.

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So now let's create an example where neither copy nor clone works.

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So we'll actually.

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Take this and we'll.

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Modify it a bit just to keep our example very similar.

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And we'll put mute Y and then we'll do a mutable ad y and then we'll also even make copy mutable.

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And then in here we are going to modify the logic being done.

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So we're going to say Y is going to plus equal X and then we want to return Y and we see that this is

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already not going to work.

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But if we run it anyway.

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We see that the value was borrowed here after a move.

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And remember that this does not work because mutable values do not implement copy or clone.

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So that is why this does not work, even though our changes were very minute.

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But all in all, closures are not overly complicated.

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And I know that this the past few lectures were more theoretical than it was hands on.

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But we will actually see where closers shine and the next topic of iterations.