Section 14 Namespace [14]_PHP Tutorial

Naming variables, functions and classes can be difficult. In addition to having to take into account the easy-to-understand name of the variable, you also have to worry about whether the name has been used somewhere else. In a small script, the second question is the basic question . When you consider reusing your code, subsequent project code must avoid using the names you have used. Generally speaking, reusable code is always contained in functions or classes, and many naming conflicts that may occur need to be dealt with. But naming conflicts can also occur between functions and classes. You can try to avoid this by prefixing all classes, or you can use the namespace statement.

The Namespace keyword gives a block of code Name. Outside this code block, scripts must reference this code block using operator:: followed by the name of the namespace. The same method is used to reference static class members. Code within the namespace does not need to declare the namespace, it It is the default. This method is better than adding a prefix. Your code will become more compact and readable.

You may wonder whether it is possible to create hierarchical (nested) naming space. The answer is no. But you can add a colon after the namespace name, and you can call variables, functions and classes that do not contain a colon in the name again. Colons are allowed in namespaces as long as they are not the first character and the last character character or followed by another colon. Colons in namespace names have no meaning to PHP, but if you use them to distinguish logical blocks, they can be a good way to illustrate the parent-child relationship in your code. -child) relationship.


/* Note: You can use this:
namespace animal:dog {}
namespace animal:pig {}

Use colons Specify parent-child relationships.
*/


You may not include anything other than function, class, or constant definitions within a namespace statement. This will prevent you from using them to improve older A function library that uses global variables. Namespaces are best suited for object orientation. Constants within a namespace use the same syntax as constants in classes.

Example 6.17 shows how to use namespaces.

Listing 6.17 Using a namespace
namespace core_php:utility
{
class textEngine
{
public function uppercase($text) file://uppercase
{
return(strtoupper( $text));
}
}

//make non-OO interface Create a non-OO interface
function uppercase($text)
{
$e = new textEngine;
return($e->uppercase($text));
}

}

//test class in namespace Test the class in the namespace
$e = new core_php:utility::textEngine;
print($e->uppercase("from object") . "
");

//test function in namespace Test the function in the namespace
print(core_php:utility::uppercase("from function") . "
");

//bring class into global namespace Import the class Global namespace
import class textEngine from core_php:utility;
$e2 = new textEngine;
?> The Import statement imports a certain part of the namespace into the global namespace.
Required To import members of a single namespace, you can specify the type as constant, function or class, and then write the name of the member;
// For example, import class XXX
If you want to import all members of a specific type, you You can use * to replace the name;
//For example, import constant * imports all constants
If you want to import all members of all types, just use *.
//For example, import *

After the member, use the from keyword plus the name of the namespace.
//For example, import class textEngine from core_php:utility;

In short, you have to write something like import * from myNamespace or import class textEngine from A statement such as core_php:utility, as in Example 6.17.

http://www.bkjia.com/PHPjc/314213.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/314213.htmlTechArticleNaming variables, functions and classes is quite difficult. In addition to taking into account that the names of variables should be easy to understand, Worry about whether this name has already been used somewhere else. In a small script, section...