Several Points to Note When Defining Command Spaces in PHP (Recommended)

1.The namespace declaration must be the first statement in the program script.In addition, all non-PHP code including whitespace cannot appear before the namespace declaration.

Below is an example of an error:

<html>
<?php
namespace MyProject; // Fatal error -　The namespace must be the first statement in the program script
?>

This is also wrong

<?php 
// Lots 
// of 
// interesting 
// comments and white space 
namespace Foo; 
class Bar { 
} 
?>

2.Cannot use PHP keywords.

Below is an example of an error:

<?php 
namespace Project;/Classes/Function; // Causes parse errors 
namespace Project;/Abstract/Factory; // Causes parse errors 
?>

3.Constants defined in the namespace.

The following MESSAGE is in the global namespace:

<?php
namespace test;
define('MESSAGE', 'Hello world!');
?>

Define2Constants defined in the test namespace:

<?php
namespace test;
define('test\HELLO', 'Hello world!');
define(__NAMESPACE__ . '\GOODBYE', 'Goodbye cruel world!');
?>

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