Why Do Some PHP Class Methods Have Leading Underscores?

Prefixing Class Methods with Leading Underscores in PHP

The use of a leading underscore in PHP class methods is a curious convention that has raised questions among developers. While some consider it a matter of personal preference, there may be some historical and practical reasons behind this practice.

Historical Origins

The apparent origin of the leading underscore in PHP class methods can be traced back to PHP 4. Before the introduction of private and protected visibility modifiers, developers relied on naming conventions to indicate method accessibility. A method prefixed with an underscore (_foo) was intended to discourage direct invocation from outside the class, albeit without enforcing any access restrictions. In some instances, developers would also use /*private/ __foo() to strengthen the intended usage.

Current Practices

Over time, the practice of prefixing all methods with underscores has diminished, with most developers reserving the underscore for private methods (starting with PHP 5.3) or protected methods (starting with PHP 5.4). However, it's not uncommon to encounter legacy code or even modern libraries that still employ the leading underscore for non-private methods, which may lead to confusion.

Practical Considerations

Even though underscores in method names no longer imply access restrictions, there are some benefits to using them judiciously:

• Visual Cue: The underscore provides a quick visual cue that a method is intended for internal use, similar to using the @ symbol for private methods in other languages.
• Code Stability: By avoiding underscores in method names exposed to the public API, developers can improve code stability by ensuring that private or protected methods are not accidentally exposed in the future.

Conclusion

The practice of using a leading underscore in PHP class methods originates from the limitations of earlier versions of PHP but has evolved into a convention for indicating internal or protected methods. While personal preference plays a role, understanding the historical and practical considerations behind this naming practice can help developers navigate legacy code and make informed choices about method naming in their own projects.

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