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OK, so this will just be a short video on what I asked you to attempt in the last video, which was

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to take this template template memory function that you created and implement it in the other derived

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classes as well, and also attempt to combine it into the overall pie of polymorphic design by trying

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to incorporate it into the base class and have it be, you know, a kind of abstracted function that

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needs to be implemented in these other drive classes.

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So let's go ahead and try then.

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So we already have it here in triangle.

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All I really need to do is copy and paste this for the base classes, so I'm going to go ahead and go

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into a circle.

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I'm going to assume in a little bit.

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I noticed last year a little bit zoomed out, so hopefully you listen too hard for you to see it, but

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I'm going to go ahead to the rectangle here.

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Assuming a bit there to pace that as well, so we can just paste it right because it's called ambiguously.

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It's bigger shape.

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This is an ambiguous argument, you know, as far as the data type, and then we're just calling area

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on whatever this shape may be, right?

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This is referring to the class.

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So that's why we can just paste it in shape since it's ambiguous shape.

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This is fine.

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Well, we don't want to change anything.

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We literally just copy pasted it in the two other derived classes.

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So what have we to here, though, in the base class and I say, OK, well, this is a virtual function

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here, pure virtual function, and this is also a pure virtual function.

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Well, I know that I want this to be in forcibly implemented into triangles, circle and rectangle,

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all three of the drive classes, you know they should all have.

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This is bigger things.

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So what if I come here and I paste this?

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I get rid of the implementation because it's not going to have something for shape that this will never

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be instantiated, right?

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But what if I say, you know, this is going to be a pure virtual function, I go here and I leave the

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template and I save virtual and create a pure virtual function, both underline and read.

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Why is it doing that?

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Well, says virtual cannot be specified on member function templates.

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If I over here.

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Yeah, it's just a tied to this whole problem right here.

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So why can I not do that?

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Well, the problem is that you cannot declare a function, both virtual and also templated, and that

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is because when it's templated, what actually happens is that it resolves the fact that there could

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be different arguments at compile time and at compile time.

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Let's say, for example, I well, let's just use this example, right?

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I have like a potentially a triangle, a circle and a rectangle that can be passed to this right?

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So a compile time was C++ compiler is actually going to do is it's going to generate generate three

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different versions of this is bigger shape function.

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So like, for example, if I go in here, what's going to happen is it's going to make an is bigger

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shape or function where this would be a triangle.

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It's going to make another version of it where this would be a circle and it's going to make another

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version where this would be a rectangle.

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So basically, it does that based on the fact that we would have three calls to this right now.

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It might only consider the circle, but let's say that we have one of these calls for each one of the

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shapes.

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So, you know, like like, I would just take triangle, for example.

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So we had it in triangle, right?

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Let's say we go back to Maine and we actually had T. Arrow is bigger shape and we put a circle in here

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and then we a T. Arrow is bigger shape.

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And then we put that rectangle right with our star and then we put T is bigger shape with our T, which

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is another triangle.

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It would generate three different functions for this scene, the template it would know like, Oh,

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I need to make three different versions of this for each type that could be passed to it.

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So that's what happens with the templating of a member function.

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It happens at compile time.

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That's when I can reach those three things the virtual, though.

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So let's go back to where the problem was right here.

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Virtual is something that kind of resolves which function to call at runtime.

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You know, when you make these virtual functions, each one of our drive classes has a different version

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of it.

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That type of resolution is something to happen at runtime, and C++ cannot handle having these two different

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time periods of resolution on which thing to call.

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They have not created support for that yet.

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And it's just really difficult to make the compiler be able to handle such things.

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So that is why you might have already noticed that this is not possible.

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We cannot put a templated virtual spiritual function inside of the base class.

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Not a total problem, though.

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We can just delete this, all this and then each one will just have its own templated function and everything

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will work fine and dandy.

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So what we'd want to do at this point is go over to you may not see be and just kind of mix and match

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this stuff.

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So.

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Maybe I'll just go in here and copy paste this.

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So let's go right here and just say if maybe are as big a shape and then we'll put like tea in there

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and it will just say on duty type with tea area.

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Is bigger than the hour type.

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With our area, and we could do it first circle as well, so I mean pace this year, and I'll just say,

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see?

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And then on this one this past like hour and we'll just say that the.

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Our Typekit, our area is bigger than the sea type.

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With the area, so now we can kind of.

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Just refer to all of them, you know, and check on all of them where there's some other random shape,

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you know, random mass and three different choices passed to it would be a bigger area wise.

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So let's go ahead and run this.

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So let's see, we only get one right now.

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Was this the circle with this area is bigger than the triangle with this area, so we go ahead and have

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to change some things.

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Let's say what if we put like one hundred here?

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So now we have one that sets a rectangle with area one one two six one six is bigger than the circle

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with Area two seventy seven point two three seven.

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Cool.

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So you notice that are still working fine when we just implemented it in the derived classes, although

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we weren't quite able to put it in here as a spiritual function like we wanted to, but that's OK.

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We can just kind of resolve it by putting it in here and just leave it in the drive classes will still

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have access to it.

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OK.

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So with that, I'm going to in this video and the next video, I'll go for what I said I would talk

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about next, which is putting the templates on the classes as well.