CODEWITHSUNDEEP
php
nocash
nocash

Reputation: 3757

What's the deal with a leading underscore in PHP class methods?

While looking over various PHP libraries I've noticed that a lot of people choose to prefix some class methods with a single underscore, such as

public function _foo()

...instead of...

public function foo()

I realize that ultimately this comes down to personal preference, but I was wondering if anyone had some insight into where this habit comes from.

My thought is that it's probably being carried over from PHP 4, before class methods could be marked as protected or private, as a way of implying "do not call this method from outside the class". However, it also occurred to me that maybe it originates somewhere (a language) I'm not familiar with or that there may be good reasoning behind it that I would benefit from knowing.

Upvotes: 174

Views: 94551

Answers (14)

Marina Tešić
Marina Tešić

Reputation: 11

That means that this method is private.

"I realize that ultimately this comes down to personal preference, but I was wondering if anyone had some insight into where this habit comes from." - it shouldn't be personal preference because every language or framework has it's own coding standards. Some FW coding standards is starting private methods with an _ and some FW discourage that.

You shoud use coding standard of a FW in which you program. To check if your code is according to the coding standard, you have a tool PHP_CodeSniffer: https://github.com/squizlabs/PHP_CodeSniffer

Very useful, detects errors regarding coding standard.

Upvotes: 0

Tassawer
Tassawer

Reputation: 39

Using underscore in just for remembering purpose that we will not 'modify the variable'/'call the function' outside the class.

As we declare const variables in all uppercase so that while seeing the name of variable can guess that it is a const variable. Similar the variable that we don't want to modify outside the class, we declare it with underscore for our own convention.

Upvotes: 3

m.ardito
m.ardito

Reputation: 391

I was looking for the same answer, I did some research, and I've just discovered that php frameworks suggest different styles:

Code Igniter

The official manual has a coding style section that encourages this practice:

Private Methods and Variables

Methods and variables that are only accessed internally, such as utility and helper functions that your public methods use for code abstraction, should be prefixed with an underscore.

public function convert_text()

private function _convert_text()

Other frameworks do the same, like

Cakephp:

does the same:

Member Visibility

Use PHP5’s private and protected keywords for methods and variables. Additionally, non-public method or variable names start with a single underscore (_). Example:

class A
{
    protected $_iAmAProtectedVariable;

    protected function _iAmAProtectedMethod()
    {
       /* ... */
    }

    private $_iAmAPrivateVariable;

    private function _iAmAPrivateMethod()
    {
        /* ... */
    }
}

And also

PEAR

does the same:

Private class members are preceded by a single underscore. For example:

$_status    _sort()     _initTree()

While

Drupal

code style specifically warns against this:

  1. Protected or private properties and methods should not use an underscore prefix.

Symphony

on the other hand, declares:

Symfony follows the standards defined in the PSR-0, PSR-1, PSR-2 and PSR-4 documents.

Upvotes: 9

user3613677
user3613677

Reputation: 31

Drupal, and using underscore:

In a general way the underscore is to simple mark the fact that a function would probably only be called by a related parent function... 

function mymodule_tool($sting="page title"){
    $out ='';
    //do stuff 
    $out  .= _mymodule_tool_decor($sting);
    return $out;
}

function _mymodule_tool_decor($sting){
    return '<h1>'.$string.'</h1>';
}

Of course, just a simple example...

Upvotes: 3

joedevon
joedevon

Reputation: 2689

I believe the most authoritative source for these kinds of conventions for PHP right now would be the PSR-2: Coding Style Guide because the Zend Framework is part of PSR:

Property names SHOULD NOT be prefixed with a single underscore to indicate protected or private visibility.

Upvotes: 77

maho
maho

Reputation: 41

In Drupal (a php CMS) underscores can be used to prevent hooks from being called (https://api.drupal.org/api/drupal/includes!module.inc/group/hooks/7).

If I have a module called "my_module" and want to name a function my_module_insert it would "hook" on the function hook_insert. To prevent that I can rename my function to _my_module_insert.

ps The way hooks works in Drupal it's possible to implement a hook by mistake, which is very bad.

Upvotes: 3

Sliq
Sliq

Reputation: 16494

Now, in 2013, this is "officially" bad style by the PSR-2 coding guideline:

Property names SHOULD NOT be prefixed with a single underscore to indicate protected or private visibility`

Source: https://github.com/php-fig/fig-standards/blob/master/accepted/PSR-2-coding-style-guide.md

Upvotes: 43

umpirsky
umpirsky

Reputation: 10024

I was strongly against prefixing private/protected methods with underscore since you can use private/protected keyword for that and IDE will mark it for you.

And I still am, but, I found one reason why it can be a good practice. Imagine that you have public method addFoo() and inside that method you have some part of task which is common with other methods addFooWhenBar(), addFooWhenBaz()... Now, best name for that common method would be addFoo(), but it is already taken, so you must come up with some ugly name like addFooInternal() or addFooCommon() or ... but _addFoo() private method looks like best one.

Upvotes: 14

Tristan
Tristan

Reputation: 1

They are called "magic methods".

Upvotes: -22

Matthew
Matthew

Reputation: 41

I know it from python, where prefixing your variables with an underscore causes the compiler to translate some random sequence of letters and numbers in front of the actual variable name. This means that any attempt to access the variable from outside the class would result in a "variable undefined" error.

I don't know if this is still the convention to use in python, though

Upvotes: 4

GloryFish
GloryFish

Reputation: 13359

I use a leading underscore in the PHP 5 class I write for private methods. It's a small visual cue to the developer that a particular class member is private. This type of hinting isn't as useful when using an IDE that distinguishes public and private members for you. I picked it up from my C# days. Old habits...

Upvotes: 10

Jeremy DeGroot
Jeremy DeGroot

Reputation: 4506

It's from the bad old days of Object Oriented PHP (PHP 4). That implementation of OO was pretty bad, and didn't include things like private methods. To compensate, PHP developers prefaced methods that were intended to be private with an underscore. In some older classes you'll see /**private*/ __foo() { to give it some extra weight.

I've never heard of developers prefacing all their methods with underscores, so I can't begin to explain what causes that.

Upvotes: 170

Quintin Robinson
Quintin Robinson

Reputation: 82325

I believe your original assumption was correct, I have found it to be common practice for some languages to prefix an underscore to methods/members etc that are meant to be kept private to the "object". Just a visual way to say although you can, you shouldn't be calling this!

Upvotes: 5

jonstjohn
jonstjohn

Reputation: 60266

Leading underscores are generally used for private properties and methods. Not a technique that I usually employ, but does remain popular among some programmers.

Upvotes: 12

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