PHP::,->, Self, $this several operators of the difference introduction _php tips

When accessing a member variable or method in a PHP class, if the referenced variable or method is declared as a const (defined constant) or static (declaring static), then the operator must be used:: Conversely, if the referenced variable or method is not declared as const or static, Then you must use the operator->.

In addition, if you are accessing a const or static variable or method from within a class, you must use self-quoted self, whereas if the internal access from the class is not a const or static variable or method, you must use the $this of the self reference.