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Welcome back to another lesson.

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We are continuing on talking about templates, but in this lesson, we're specifically going to talk

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about class templates.

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And yes, you heard that right.

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You can also use templating on classes, not just on member functions.

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So why would we want to template a class?

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Well, you might encounter a scenario where you want to make some sort of class.

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And you want to, let's say, have that glass door like a container of something, or maybe it has some

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data members that you define and the thing is, is that you want those data members to be able to take

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multiple times, potentially without having to make a different type of code, like what if it's, you

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know, we have, for example, like you see, I've declared a pear shaped list agent statelet, simplest

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IACP.

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So what if we have a list of shapes, but we're not really sure what type of shape it's going to be?

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So what I mean by that is that maybe we want the ability to maintain a list of triangles or instead

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a list of rectangles or instead a list of circles.

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So of course, you could just make a vector and store that in there.

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But what if we wanted to make some additional functionality that would be calculated automatically for

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us?

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Like, maybe this shapeless class could have a function that found the largest area of the shapes in

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that list that it had.

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So let's say it, the shapeless class.

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It has a vector of shapes and maybe, for example, its circles.

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It would find you have some function that could find the circle with the largest area out of that list

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of circles.

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But what if you wanted it to do the exact same thing for rectangles all of a sudden or triangles?

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You'll be annoying for you to have to make like a shapeless circle class and a shape list, rectangle

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class and a shapeless triangle class.

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Just so you can have the same thing, we are doing polymorphisms so we might be able to just use like

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the base class shape, but there's also kind of an easier and more intuitive way by using templating.

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So let's go ahead and kind of show what's going on here.

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So instead of me template right away, let's just make a class called shape list.

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What I'm going to do is for the public, and I'll put a private section and let's say we want this vector

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of shapes, right?

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So I say, Vector, come here and I like Vector.

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And let's say I call it a vector shape underscore shapeless like this and come back here and I'm like,

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Well, what do I put for the type of the vector?

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I don't want to put circle, because then it would only be able to handle circles.

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I don't want to put rectangles and could only do that same for triangle, right?

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And I'm not including those up here yet either.

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So how would I make it be a vector that could handle any one of those things?

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Or let's say that I even come up with another shape that somehow, you know, doesn't inherit from this

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shape thing, too?

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Maybe I come up with a class called line, and it just holds like a bunch of different lines, and it

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can tell me like the distances of the lines or something.

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So it's not even inheriting from shape.

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So we couldn't even use like a basic shape.

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Here is the type of the vector, right?

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It would just be like its stand alone line class, but we still wanted it to somehow be able to have

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a list of lines and consider that to be OK being in the shape list, right?

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So there's a way we can do this, and it's by using template, of course.

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So just like we have done with the functions, I'm going to write the word template and say Class T.

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But it's going to go on top.

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You notice here it's on top of the class definition.

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So this will enable it so I can put that data type of T in the vector here.

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And so this will make it so we can have a vector of circles or instead a vector of squares or sorry

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rectangles or triangles without having to make a separate class for each one, we can reuse the same

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class for different data types.

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So the cool thing about being able to temper the class is it lets us have some data members here that

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could potentially be different types, you know, we also might have something, let's say like, you

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know, each like shapeless, like the shapeless that we have.

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Let's just say like, you know, we have something called like a current shape and this type of team,

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we just say like T current, let's say, current shape type or just do like underscore

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something like this.

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So maybe we are not sure whether it's going to be a.

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Circle or a square, something we want to like, take one of the shapes, right?

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So if it's a circle, we'll just take like the first circle in the vector and we'll set it to like,

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you know, current shape or something.

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I don't know, but I'm not going to leave this here.

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But just to illustrate the fact that you could do this right, we can even have it declared as a data

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type T in our private data remember section.

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And just because we've put this template here.

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So I'm not going to keep that there because it doesn't seem very sensible.

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I'm going to have this vector of type T was the class template type so it can accept anything that comes

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into it.

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So what else should we put in this class?

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I'm going to go ahead and put on a constructor, right?

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So I should say shape list.

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And then what if we have some cool methods, maybe like I say, like prints, print list or something

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like that?

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And this'll just like, you know, print the shape list out.

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Maybe I say that like largest shape, right?

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So what if I want to say?

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Look, I want to say that we will return the largest shaved or something like that, so I could say

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that we will do so return T and I will say like get largest shape, maybe get larger shape out of that

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vector.

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So it'll, you know, find whatever shape it is and return the largest, the one with the largest area.

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And we'll, of course, maybe want something to add it to the list, right?

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So what if I say add shape, right?

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And then this will take in some type of shape.

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We're going to use Ti again because we're not sure what the shape type might be.

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We're just going to use our template type for that.

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So let's say the parameter will be typed.

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So I'm just going to say shape right here.

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I'll say s.

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Cool.

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So this kind of gives us everything here.

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And so one, before I generate these function definitions, I want to kind of point out some important

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details.

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So one thing that we're going to have to do if we have the template here in the header file and we have

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a separate zip file is that this may seem weird, but instead of us putting like some of them in here

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instead of us doing in the CBP include the shape forms and spell.

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That right include shape, Lester age.

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We're not going to put that in here.

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Instead, we're going to do the complete reverse.

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And here we are going to say

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include down here and we're going to say shape list dot CVP.

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And why are we going to do that?

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Well, it's a problem with the templating, if we template the header file here and we decide not to

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put the implementation in the same file.

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Then things have to be flipped around, so the compiler will know how to generate everything correctly.

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So for that reason, you have to have the definition here in the header file.

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So put all your prototypes and everything in the header file here and underneath that, but before the

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macro guard stuff finishes.

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So, you know, you make sure to put this as well.

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Put your macro guys.

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But before you have this, and if and after the class definition, you should have it include and then

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the CPE implementation file.

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You also can just ignore, you know, totally not new separate files.

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And if you wanted to, you could erase this, you know, and just take everything that you would put

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in this heap and just start, you know, typing it right here, you know, paste it right.

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There have all the implementation in the same file, and that's totally fine as well.

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I just want to show you how you can do it both ways, you know?

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So I'm going to include this checklist CBP here.

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Another important thing about Sea Lion is that you're going to want to make sure that the shape lists

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H and shape list copy whatever the template files are.

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You know, anything that has to do with templates if they're in separate files.

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Of course, you're going to want to have to go one or want to go over here to see make lists, and you're

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going to want to make sure that they're not listed here in this ad executable section.

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They should not be added as targets to the build process.

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You know, this is what this is.

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The build process like a file, one of the files that's needed to successfully compile the projects

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here and you list your target files to compile, but you're not going to want to have shape list or

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shape list CPP listed in here.

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Otherwise, it's most likely going to throw some errors.

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So I want to point that out as well.

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So if you're not working on here, just make sure that you're like, if you're using some other type

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of make file or something to compile, just make sure that you're including only the other files as

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targets.

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This will just be considered a library.

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It'll work out.

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Don't worry, the CP doesn't need to be compiled because this is being included here instead.

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All you have to do.

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I'll show you this once we get to main is just include the header and main.

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And it's automatically just going to all work out, it'll go through here, it will use it as like another

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library that gets imported without you having to compile it and have these files as targets so don't

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don't include them as targets.

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So let's go ahead and generate some ecotourism and generate a definition.

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And it's not putting it in the air, so let me just generate it and copy it, so I'm going to go over

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here and I'm just going to copy it here and then I'll go here and generate this definition.

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All right, cool now it went ahead and put it in there.

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I don't want it to include this, though, so I'm going to get rid of that once I once I do this, so

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generate a function for this.

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And let's go ahead and generate a function for this.

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Cool.

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So what I'm going to do now is go up here and definitely get rid of this because we don't want to include

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that.

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And so you notice that when I generated it, it put this template class T on top of the member functions.

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Also notice that it went ahead and instead of just putting shape list for the scope resolution part,

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you know, here's the scope resolution operator for the name of the class input shape list and T right

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here.

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So this is another part of the syntax.

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If I click this right here, it will expose this template.

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So this is another part of the syntax that's important.

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So when you do this class, every function, even though you're not really thinking about them as being

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templated functions, you need to have a template syntax.

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And this is well on every one of the member functions here.

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OK.

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And that does this.

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Regardless of whether you're using separate files or putting the implantation in this header file,

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you're still going to need this template class T over all the functions, and you're still going to

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want to put this part here for this scope resolution.

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So just want to make sure that that's very clear.

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All right, cool.

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So you notice this stuff highlighted just because I'm already using this in Maine and I'll show you

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the code that I'm using in that client file.

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So let's go ahead and implement some of the logic for this stuff right here.

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So I'm going to come in here for shape list what I actually want to do.

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I'm going to make an initialization list for this constructor, and I'm just going to say shape list

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or vector should just be a new vector of type T.

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Like this?

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I'll use the Vector Ops Vector Constructor, right?

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So this is going to be my initialization list style constructor.

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So this will make a new vector here of type T and set our data member shapeless to that.

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So add shape takes shape and all we're going to do is, say, shapeless start, push back and s.

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And so this is type T, right?

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This is already Typekit here here.

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So it's going to be able to add that, OK, cool work for any shape for this print list I'm going to

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go through.

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I will do kind of an item based loop here with the auto keyword.

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So I'll just say auto S4 shape in shape list and then I'll go ahead and see out the let's see.

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We'll do the shape list color of maybe first.

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So I'll say s dot

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get color and get color.

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Is that what it is?

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Get color.

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Okay, cool.

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Escort get color so this can be like blue, and then let's say like we do a little space and then we'll

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say, like an escort.

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Is it type?

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She was going here to see that type.

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Right.

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So type, so this could be like, you know, like blue rectangle,

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and we'll just say with area and I'll say S-type area.

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And then we'll do an incline.

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Cool, so I just want to print out some info about each shape, right?

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So I have this kind of bass loop.

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I'm using the other keyword, so it resolves to the type.

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And then it goes through shapeless Australian, and so for every shape in the shape list, it's going

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to say the shape, get color.

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So for example, this could be blue and then a space, and that's going to say the type.

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So like Blue Circle Width area, and then it'll print out the shapes area so we can print out all the

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info and loop through all the list of the shapes that we have.

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You get larger shape.

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I think I'm going to do something like where I make some temporary variable and it's just going to come

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called like the largest in index or sea index.

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So how about I say largest index equals zero?

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So we'll start at zero and then I'll say four and I equals zero is less than

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shapeless size I have plus plus.

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And then what we'll do is say if let's see.

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So if shape list I.

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Dot area is greater than the shape list and the largest index dot area.

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So what I'm checking right here is I'm saying like it's the current shape that we're on and the list

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is it's area greater if its area is greater than.

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The largest one so far, right?

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So I start watching this is zero, but I'll just keep updating the largest one.

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So I'm saying if it's larger than the current largest, then we'll just go ahead and save it.

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The largest index equals I will change the index of that right?

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And then that way we can update that.

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Update the index as the largest one.

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Cool.

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So, otherwise, it'll just keep going through, and then at the end, I'll just say return ship list

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and I'll say largest, I'd say the largest index, so that would be able to get the largest shape for

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us.

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And I think that's kind of all I want to add right now.

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Yeah.

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So we will go over to Maine now, and we'll kind of test some of the stuff out.

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I already have some code there.

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I'm going to change a little bit because I kind of renamed this.

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So let's go ahead and check this out.

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So I kind of have these pointers left here, but I'm going to make some more variables that aren't pointers.

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So I have like some circles and rectangles, for example.

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And so let's talk about how we can now make a shape list object.

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So first of all.

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You're going to want to include the simplest header up here, just like any normal header, like, you

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know, these ones.

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And then what I'm doing is first, I'm making, like I said, some non pointer objects of rectangle

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and circle.

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I go here and I say shape list, and then I put the type here.

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The explicit type here because shapeless expects since templated, it's kind of like a vector, right?

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It expects you to put the type that you want to be associated with the class.

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So this object, this shapeless object I'm calling SLC for shapeless circle is of type circle.

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Yet I'm still able to use the shapeless class to create a rectangle version of it.

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And I have a special object now that is shapeless rectangle.

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So this area after so here's the class name, right data type name.

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But also a part of that is the template.

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So you put the class name, then you put the template type in the angle brackets and then you can put

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the name of the variable right in the variable name.

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Same thing here for rectangle, right?

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So I have two different types shape list circles, shapeless rectangle, and I'm calling them appropriately.

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And the way that I'm doing that is through this angle bracket template type here.

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So I'm going to change this to print list instead of print shapes, assistance or other stuff earlier,

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so we're going to change this to print list.

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What else should we do?

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Maybe we can say largest shape or something like that, so.

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Maybe it will print the area of the largest ship.

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So let's just say we print the list and then after this, we'll say, like SLC.

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Uh, let's see.

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See, see out SLC.

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Dot.

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Uh, get larger shape.

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Dot area.

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How about that?

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And I will put this.

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Copy paste this here and after this print list, I'll just change it to SLR so I can get the largest

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of the rectangles too.

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So you notice I'm also d referencing one of these pointers up here.

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So this circle I just consider see one in this rectangle I was considered kind of like as if it would

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be R one, but I'm using the pointers.

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But what I'm doing is I'm passing them as d referenced to this shape because you know that over here

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we when we add the shape, we expect it to not be a pointer just to be, you know, a normal object

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of type T..

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You can also do it with pointers to we could rearrange this and do it.

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But just for simplicity of step, I think I'm just kind of like doing it like this.

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So let's go over here.

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So you notice there, I d reference that that's why this star is there.

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Same for the rectangle just referencing these pointers up here so I can pass a normal object.

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Let's go ahead and run this and see what we get.

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OK, so pretty cool, right?

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Let's go ahead.

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Let me zoom in on this here.

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So we get a green circle with Area 277, Blue Circle with Area 47 and Black Circle with Area 191.

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We see that the biggest one was 277, so that worked out and found the correct one.

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You know, the rectangle as well.

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We see all these.

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And it found the largest one for the rectangle as well.

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So let's just compare that to what we were up here.

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Seems to be pretty good, at least these are.

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Correct, right, so we have a green of blue and a black green, blue, black and red and purple purple,

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purple.

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These are all purple.

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So pretty cool.

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So I didn't test it with the triangle, but it totally be fine with the triangle as well.

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I used the print list, the ad shape and the get larger shape, so we tested all three of those.

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And so the main takeaway is just the syntax here and the idea that you can use the template on a class

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as well.

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So it's definitely a powerful tool.

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Templating is kind of one of the coolest things that you can do in C++, and it really makes it a kind

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of competitor with some of the more modern languages that kind of have these automatic and more dynamic

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systems with typing and stuff like that.

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So with that, I am going to leave you with what we talked about so far in this lecture and not go any

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further with this, but you should be able to look back on this and understand how to deal with the

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templated classes as well.

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Remember some of the important points that are kind of little important details like including the copy

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in the header, rather than including the header in the CP whenever you're doing separate files for

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the templates.

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Also, if you're using Feli and make sure to not have those two files in the targets if you're doing

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separate files and that means don't have them in this list here in the see make lists.

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And if you're working in something else, just don't have them in the targets to whatever the building

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process is, if you're using make and making make files.

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Good for you, but just don't put those targets.

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And just to let you know you can take all the CBP code and just remove this highlighted line and put

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it in here and have it all in one file.

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So with that, we are nearing the end of this half, first half of the course.

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We've talked about almost everything there is in basic programming and syntax for C++.

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I am going to have one final project for you to do.

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And then after that, there will be the second half of the course, which will be all about data structures

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and algorithms.

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We will continue using C++ and we will be putting a lot of this stuff to use.

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In fact, we will be using templating for the first data structures that we go over.

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We will need to use templates to deal with those.

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We're going to use that just so we can practice as well.

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So you feel comfortable, more comfortable with templates as we move on.

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We won't be using templates all the time, but we will try and get some practice.

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So you feel comfortable.

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OK.

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So with that, I will see you in the next lecture.