A namespace is a declarative region that provides a scope to the identifiers the names of types, functions, variables, etc inside it. Namespaces are used to organize code into logical groups and to prevent name collisions that can occur especially when your code base includes multiple libraries. All identifiers at namespace scope are visible to one another without qualification. Code in header files should always use the fully qualified namespace name.
The following example shows a namespace declaration and three ways that code outside the namespace can accesses their members. The using directive allows all the names in a namespace to be used without the namespace-name as an explicit qualifier. Use a using directive in an implementation file i. If a local variable has the same name as a namespace variable, the namespace variable is hidden.
It is an error to have a namespace variable with the same name as a global variable. A using directive can be placed at the top of a. Always use fully qualified names in a header file. If those names get too long, you can use a namespace alias to shorten them.
See below. Typically, you declare a namespace in a header file. If your function implementations are in a separate file, then qualify the function names, as in this example. Because we want the interfaces and classes here to be visible outside the namespace, we preface them with export. Conversely, the variables lettersRegexp and numberRegexp are implementation details, so they are left unexported and will not be visible to code outside the namespace. In the test code at the bottom of the file, we now need to qualify the names of the types when used outside the namespace, e.
Even though the files are separate, they can each contribute to the same namespace and can be consumed as if they were all defined in one place. As shown in the program, we can access the function fun by using the operator as nofun. In the program above, we can see how we can create several namespaces with the same name. The name sample has been used by two namespaces that have different variables. Therefore we have variables in the same scope, within both of them. We can also see how to define the unnamed namespace and access the function fun.
In the program above, we can see how nested namespaces are declared and accessed from outside of the namespace. We also demonstrated the way we access a variable in the namespace without the scope resolution operator :: and use the using directive. We have also seen how we can create the namespace myalias that allows us to use it explicitly using the name of the alias. We have seen the benefits of using namespace in our programs, with our examples above. By using namespace, we can prevent conflicts in files with the same variable names and function names within the same program.
Peer Review Contributions by: Saiharsha Balasubramaniam. Dawe is passionate about innovation, new technology and software development. Dawe is particularly motivated in learning all about android and wants a future full of it. A namespace allows you to place a bunch of code under a name and not have any naming conflicts with classes, functions and constants.
People got up in arms because it is also used as an escape character. You can find a lot more information on the official PHP documentation for namespaces. There is a controller class with the name: Controller. So how can a class extend another class that has the same name? Also note that namespace is case-sensitive. There are techniques like namespaces in other programming languages like packages in Java. They are used to be able to have mutliple classes with the same name wihtin a project.
What are namespaces? In the broadest definition namespaces are a way of encapsulating items. This can be seen as an abstract concept in many places. For example, in any operating system directories serve to group related files, and act as a namespace for the files within them. As a concrete example, the file foo. In addition, to access the foo.
This same principle extends to namespaces in the programming world. A Namespace works like a directory. You know how you can put files in a directory with the same names as files in the parent or any other directory? Well, a namespace lets you do that within an application for variables, functions and classes. There was a bit of a trend in PHP a little while ago for huge classes of static functions. The only way to call any of those functions was by prefixing a call with the class name.
This was a primitive attempt at namespaces, but with not very much of the benefits. Much like directories and files , namespace in PHP serves to group classes , functions , interfaces and constants. It provides a way of wrapping items from the global space and allows use of plain item name without causing name collision in a program. It's supported in PHP 5.
Namespace is like packaging many things into a single pack. Imagine a namespace as a drawer in which you can put all kinds of things: a pencil, a ruler, a piece of paper and so forth. To avoid using each other's items, you decide to label the drawers so it's clear what belongs to whom.
A namespace basically lets you put code into a container. This will prevent problems with two functions as well as classes and variables that share the same name.
These are useful when working when larger applications to prevent issues with pieces of code sharing the same name. For example, lets say we wanted two functions called "TheMessage". These both would print echo different messages each. Normally, this would cause a syntax error, as you cannot have two functions that share the same name.
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