PHP OOP: What's the Difference Between `::` and `->` Operators?

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Understanding the Difference Between :: and -> in PHP

When working with objects in PHP, you may encounter two operators: :: and ->. Although they appear similar, these operators serve distinct purposes in accessing methods and object properties.

:: (Double Colon) Operator

The :: operator is primarily used for accessing static members of a class. Static members are declared using the static keyword within a class definition. They belong to the class itself, not to individual instances of the class.

The following code accesses the static property $prop_static of the B class:

B::$prop_static;

:: can also be used to resolve scope and call static methods of a class:

B::func_static();

-> (Arrow) Operator

The -> operator is used to access instance members of an object. Instance members are declared without the static keyword and are specific to an instance of the class.

To access an instance property, use the -> operator followed by the property name:

$b->prop_instance;

Similarly, -> can be used to call instance methods:

$b->func_instance();

Key Differences

• :: is used for static members (variables and methods), while -> is used for instance members.
• :: is used for scope resolution, while -> is used to interact with actual object instances.
• While :: is generally used for static members, there are exceptions where it can access instance members (e.g., calling the parent method from within an instance).
• The -> operator is not only used for assignment but also for accessing object properties and calling methods.

Conclusion

Understanding the difference between :: and -> is crucial for effectively working with OOP in PHP. By adhering to the appropriate usage guidelines, you can leverage both operators efficiently to access class members and manipulate objects.

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