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Declaring namespaces

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A namespace declaration can look as follows:

It is recommended to only declare a single namespace per file, even though you can declare as many as you like in a single file: 

namespace First {
    class A { ... }; // Define class A in the namespace First.
}

namespace Second {
    class B { ... }; // Define class B in the namespace Second.
}

namespace {
    class C { ... }; // Define class C in the root namespace.
}

Every time you declare a namespace, classes you define after that will belong to that namespace: 

namespace MyProject\Shapes;

class Rectangle { ... }
class Square { ... }
class Circle { ... }

A namespace declaration can be used multiple times in different files. The example above defined three classes in the MyProject\Shapes namespace in a single file. Preferably this would be split up into three files, each starting with namespace MyProject\Shapes;. This is explained in more detail in the PSR-4 standard example.

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Namespaces:
* Namespaces
* Declaring namespaces
* Referencing a class or function in a namespace
* Declaring sub-namespaces
* What are Namespaces
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0 Getting started
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3 Functional programming
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