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In this lecture you will learn about the using namespaces.

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So namespaces gives you a mechanism to modularize code.

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So a namespace allows you to label your types, functions and variables with unique name so that using

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the scope resolution operator, you can give a fully qualified name.

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So the advantage is that you know exactly which item will be called.

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And the disadvantage is that using a fully qualified name, you are in effect switching of cplusplus

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arguments, dependent lookup mechanism for overloaded functions where the compiler will choose the function

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that has the best fit according to the arguments passed to the function.

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So defining namespace is simple.

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For example, let's define a namespace here.

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Namespace you will use the namespace keyword.

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You decorate the types, functions and global variables with the namespace keyword here and the name

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you give it to it.

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So let's create a utilities namespace.

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Here.

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And.

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Here.

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So let's create a function in this namespace pool.

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Pool Data.

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Pool data.

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Here.

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Let's make this, for example, just the comment, the code here, and then let's add another function

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here.

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Integer Get data.

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Get data.

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Let's add another comment here because we will fill these codes in later lectures.

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Code.

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Here.

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So as you can see here, we created a code, for example.

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Example code two and example code.

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Example Code one.

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And then you don't use the semicolon after declaring an ending.

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Namespaces here.

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So now you use this symbols here.

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For example, if if utilities namespace pool data returns true, then you will get the then you create

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the integer number, utilities get data.

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And here let's add an example.

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We will use E.

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Variable here.

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So then the namespace declaration may just declare the function.

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So in which case the actual functions will have to be defined elsewhere.

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So and you will need to use the qualified name here.

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Uh, let's.

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Uh, make it here.

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Um.

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You can do this like this.

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For example.

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Namespace.

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My professional.

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Your utilities.

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Usually it's not best practice to make your variable names that long, but that's okay.

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This is just an explanatory code here.

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Then.

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And then let's create a declare the functions declaring the functions.

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Here, Bull.

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Uh, pool data.

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Pull data.

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And integer get data.

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As you can see, we can declare the same function names because of that.

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These two utilities doesn't have to do with each other, so they are in the different namespace.

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So you can declare the same named functions here because they are they they don't have to interact with

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each other.

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So.

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Then we can create a bool here.

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For example, let's define the bool.

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Here.

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Bull utilities or not here.

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You can define this code later.

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Defining the functions later.

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Here.

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Defining the functions here.

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So bool utilities here.

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As you can see, we adhere to double dots here and pull data.

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And then you can write the.

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Code that returns bool returns a bool from this function.

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And we can create the get data after as soon as you can see here, this is the integer.

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So integer ops, we have a problem here.

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Let's see, what is this?

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Can you define or declare pull data here?

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Because name does not includes namespace utilities.

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As you can see, we can not use the.

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Another.

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As you can see, there is a different namespace.

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So we need to add here my professional utilities and as you can see here, error is gone.

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So let's add another rule here.

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Not this is an integer.

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I'm sorry, integer.

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Um, okay.

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My professional utilities get data.

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And code that returns an integer in this function.

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So one use of a namespace is to version your code.

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So the first version of your code may have a side effect that is not in your functional specification

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and this technically bug.

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So.

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But some colors will use it and depend on it.

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When you update your code to fix the bug, you may decide to love to love your colors.

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The option to use the old version so that your code does not break.

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So you can do this with a namespace, but before that.

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I want to hear.

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Let's use only my professional code.

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So I just commented this code and you can use later here.

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And.

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Let's go to our namespace version two here.

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Okay.

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Namespace my profession Utilities.

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And then let's create a version two in this namespace.

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So.

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Namespace namespace v2.

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And then you can declare your functions again.

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And here.

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Uh, pool data.

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And the integer get data.

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Here.

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Integer knife feature.

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New feature.

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Here.

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So now, here.

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Now colors will want to specify.

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It's actually make our new with version two program.

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So this colors who want to specify version can call the fully qualified names for example colors could

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use here my professional functions.

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Two.

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And here pull data.

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As you can see here, there's no problem.

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So we can use this namespace inside the namespace.

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So to use the so we can use this newer version and utilities pulled data.

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My professional utilities pull data to use the older version so we can use this is the new version version

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of our namespace and we can use the professional.

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My.

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Officer, we have to end quote here.

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My professional utilities just then the first version.

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So as you can see, we are using pool data now and let's use the pool data.

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So there is a different functions in same namespace.

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So when an item in a specific namespace calls an item in the same namespace, it does not have to use

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qualified name.

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So if the new feature here, new feature here, functions calls, get data, it will be here.

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My professional.

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My professional.

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A utilities here.

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The V2.

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Need to get data.

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Get data.

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Yes.

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And that is the cult here.

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So.

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So it's important to note that to declare a nested namespace, you have to do the nesting manually as

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shown here.

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So let's create an example to write the first version of the code that will call it using the namespace

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utilities.

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So C plus plus 11 provides a facility called an inline namespace that allows you to define a nested

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namespace, but lost the compiler to treat the items as being in the parent namespace when it performs

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an argument dependent lookup.

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So let's create an inline namespace here.

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Okay.

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Inline namespace.

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We won.

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We?

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Yeah, we won version one.

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And.

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Here.

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Pull.

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Pool data.

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Pool data and integer.

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Get data here.

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And as you can see, we have namespace v2.

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Also, let's actually add before we v2.

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So we can it's more readable.

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So now to call the version of get data here, as you can see, we got an error here.

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Is ambiguous.

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So now to call the first version of get data, you can use the utilities get data or utilities.

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We one.

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Full data.

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As you can see here, it's fixed.

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V1V1.

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Get data.

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And utilities.

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We want pool data so fully qualified names can make the code difficult to read, especially if your

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code will only use one namespace.

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So to help you here you have several options.

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You can place a using statement.

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Um using statement to indicate the symbols declared in the specified namespace.

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The namespace can be used with a fully qualified name.

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So for example, you can use the using a namespace utilities.

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My professional.

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My professional utilities.

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And like that.