Differences in usage of ::, ->, self, and $this operators in PHP

When accessing member variables or methods in a PHP class, if the referenced variable or method is declared as const (defining constant) or static (declaring static), then the operator:: must be used, otherwise the operator must be used ->.

In addition, if you access const or static variables or methods from within the class, you must use self-referencing self, otherwise you must use self-referencing $this.

In fact, if you have mastered the relevant knowledge of static classes, static variables, and constants in PHP, these are not difficult to understand.