Скачать или смотреть PHP magic constants in action

PHP Magic constants are predefined constants that change value depending on where they are used.

There are 9 magic constants. Magic constants are started and ended with double underscore, except constant ClassName::class.

Here are 9 magic constants with their description.

1. _CLASS_
If used inside a class, the class name is returned.

2. _DIR_
The directory of the file is returned.

3. _FILE_
The file name including the full path is returned.

4. _FUNCTION_
If inside a function, the function name is returned.

5. _LINE_
The current line number is returned.

6. _METHOD_
If used inside a function that belongs to a class, both class and function name is returned.

7. _NAMESPACE_
If used inside a namespace, the name of the namespace is returned.

8. _TRAIT_
If used inside a trait, the trait name is returned.

9. ClassName::class
Returns the name of the specified class and the name of the namespace, if any.