This is the self parent in PHP

This is a pointer to an object instance, which is determined when instantiated;

Self is a reference to the class itself and is typically used to point to static variables and constants in the class;

The parent is a reference to the parental class, and the parent is generally used to invoke the constructor of the parents.

A member of a class that uses static (the generic keyword static) must be called with self. Using self to invoke a static variable must use:: (Field Operation symbol).

The static keyword describes a member that is static and can only be used with the class name and self: access, the value can be changed, the definition needs to add the $ symbol, you can use the private and other modifiers.

Const is used for class member constant definitions and can only be used with the class name and self:: Access, values cannot be changed, the variable names are generally capitalized when defined, and modifier words such as private cannot be added.

private static $count = 0;//defines a static property const VERSION = 2.0;//defines a constant

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