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In this video, we'll learn about friends of a class in c++.

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Friends have always been a controversial topic in c++.

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The controversy is about encapsulation.

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And whether friends violate encapsulation or enhance it.

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You can decide where you are on this issue.

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But friends are indeed part of the c++ language and it's important to understand them.

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So what is a friend of a class?

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A friend of a class is a function or another class

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that has access to private class members.

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And that other function or class is not a member of the class that it's accessing.

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In the case of friend functions,

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these can be standalone functions or member methods of another class.

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And in the case of another class,

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the entire class will have access to the private information of the class granting friendship.

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So as you can see, friends have unfettered access

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to both public and private data members of a class, but they're not members of the class.

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It's important to understand how c++ treats friendship in the big picture.

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First, friendship must be granted, not taken.

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A class must explicitly declare its friends in its class declaration using

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the friend keyword. Friendship is not symmetric.

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So if a is a friend of b, that doesn't mean that b is a friend of a.

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This must be explicitly granted.

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Friendship is not transitive.

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if a is a friend of b and b is a friend of c,

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then a is not a friend of c, again unless specifically granted.

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And finally, friendship is not inherited.

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So what does declaring a friend look like in c++.

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Here you can see the case of declaring a standalone non-member

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function as a friend of the player class.

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Notice that the player class grants the friendship by declaring the function prototype

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preceded by the friend keyword.

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That's it. Now the display player function has access to

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everything in the player class.

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So in the display player function,

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we don't have to go through public getters or setters to display the player information

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or set player information.

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We can directly access the private class attribute.

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In fact, we can change them as well if we wanted to

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since the object is passed by reference and in this case non-const.

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Let's see how we would declare a method in another class as a friend.

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In this case, we're declaring the display player method

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of the other class as a friend.

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That method will now have access to everything in the player class.

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And that method might be implemented as follows.

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Notice that it is indeed a member of the other class.

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But you can use the player class's private attributes directly within it.

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Finally, we can declare an entire separate class as a friend.

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In this case, we declare the class other class as a friend of player.

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So all the methods in the other class will have access to the player classes private attributes.

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As you can see friendship is very powerful,

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it can bypass function call overhead associated with getters and setters

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setters and other class methods and allow direct access to private attributes.

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Sometimes we have classes that use other classes

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and writing code using getters and setters becomes long

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tedious and sometimes gives you overhead.

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However, that shouldn't be the only reason for granting friendship.

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Friendships should be granted only when it makes sense in the design of your system

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and then only the minimal necessary friendship should be granted.

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We'll see friend functions again when we use operator overloading in the next section.