My question is rather simple, here is the context:
http://php.net/manual/en/language.oop5.magic.php
Magic Methods
The function names __construct(), __destruct(), __call(),
__callStatic(), __get(), __set(), __isset(), __unset(), __sleep(), __wakeup(), __toString(), __invoke(), __set_state() and __clone() are magical in PHP classes. You cannot have functions with these names in
any of your classes unless you want the magic functionality associated
with them.
PHP reserves all function names starting with __ as magical. It is recommended that you do not use function names with __ in PHP unless you want some documented magic functionality.
I get what these methods are for and how to use them. What I don't understand is this:
...unless you want some documented magic functionality.
What does that even mean? Are there actual reasons to create user defined __magicMethods()?
I think that they only mean that it's better not to use __ as a starting name for your methods because PHP has reserved that convention for his magic methods and if you do use that for a method it might get overriden in the future and have some magic functionality. At least that's how i understood that
EDIT - to be even clearer: Let's say thatyou implement for your own business logic a method called __toNumber(). In a future version of PHP they decide that whenever an object is used as a number (maybe when you do $result = 3 * $yourObject) the magic method __toNumber() will be invoked...your object will have some "Magic" documented functionality even if you didn't specifically add it
It means never use names that starts with __ for functions unless you want the magic functionality documented in the PHP manual.
Related
I know there are a couple of similar questions here in StackOverflow like this question.
Why is overriding method parameters a violation of strict standards in PHP?
For instance:
class Foo
{
public function bar(Array $bar){}
}
class Baz extends Foo
{
public function bar($bar) {}
}
Strict standards: Declaration of Baz::bar() should be compatible with
that of Foo::bar()
In other OOP programming languages you can. Why is it bad in PHP?
In OOP, SOLID stands for Single responsibility, Open-closed, Liskov substitution, Interface segregation and Dependency inversion.
Liskov substitution principle states that, in a computer program, if Bar is a subtype of Foo, then objects of type Foo may be replaced with objects of type Bar without altering any of the desirable properties of that program (correctness, task performed, etc.).
In strong-typed programming languages, when overriding a Foo method, if you change the signature in Bar, you are actually overloading since the original method and the new method are available with different signatures. Since PHP is weak typed, this is not possible to achieve, because the compiler can't know which of the methods you are actually calling. (hence the reason you can't have 2 methods with the same name, even if their signatures are different).
So, to avoid the violation of Liskov Substituition principle, a strict standard warning is issued, telling the programmer something might break due to the change of the method signature in the child class.
I know I am late to the party but the answers don't really spell out the actual problem.
The problem is PHP doesn't support function/method overloading. It would be difficult to support function overloading in an untyped language.
Hinting helps. but in PHP it is very limited. Not sure why. For example you cannot hint a variable is an int or Boolean yet array is fine. Go figure!
Other object orientated languages implement this using function overloading. Which is to say the signature of the function is obviously different.
So for example if the following was possible we would not have an issue
class Foo
{
public function bar(Array $bar){
echo "Foo::bar";
}
}
class Baz extends Foo
{
public function bar(int $bar) {
echo "Baz::bar";
}
}
$foo = new Baz();
$bar = new Baz();
$ar = array();
$i = 100;
$foo->bar($ar);
$bar->bar((int)$i);
would output
Foo::bar
Baz::bar
Of course when it came to constructors the php developers realised they have to implement it, Like it or not! So they simply suppress the error or not raise it in the first case.
Which is silly.
An acquaintance once said PHP implemented objects only as a way of implementing namespaces. Now I am not quite that critical but some of the decisions taken do tend to support that theory.
I always have maximum warnings turned on when developing code, I never let a warning go by without understanding what it means and what the implications are. Personally I don't care for this warning. I know what I want to do and PHP doesn't do it right. I came here looking for a way to selectively suppress it. I haven't found a way yet.
So I will trap this warning and suppress it myself. Shame I need to do this. but I am strict about STRICT.
You can override parameters, but the signature should match. If you had put Array out in front of $bar, there would be no problem.
For example, if you had added an additional parameter, there would be no problem, provided the first parameter had the same type hinting. This is good practice in any language.
Because you declared on Foo that $bar should be of type array, while in the extending Bar, $bar's type isn't declared.
This isn't an error, it's a warning. You should make the method definition compatible with the original, base class. You can, however, safely ignore it if you know what you're doing (and only if you know what you're doing!!!)
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.
Any thoughts, insights and/or opinions would be appreciated.
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.
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.
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
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.
Leading underscores are generally used for private properties and methods. Not a technique that I usually employ, but does remain popular among some programmers.
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...
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:
$_status _sort() _initTree()
While
Drupal
code style specifically warns against this:
Protected or private properties and methods should not use an underscore prefix.
Symphony
on the other hand, declares:
Symfony follows the standards defined in the PSR-0, PSR-1, PSR-2 and PSR-4 documents.
I believe your original assumption was correct, I have found it to be common practice for some languages to prefix an underscore to methods/members etc that are meant to be kept private to the "object". Just a visual way to say although you can, you shouldn't be calling this!
I know it from python, where prefixing your variables with an underscore causes the compiler to translate some random sequence of letters and numbers in front of the actual variable name.
This means that any attempt to access the variable from outside the class would result in a "variable undefined" error.
I don't know if this is still the convention to use in python, though
In Drupal (a php CMS) underscores can be used to prevent hooks from being called (https://api.drupal.org/api/drupal/includes!module.inc/group/hooks/7).
If I have a module called "my_module" and want to name a function my_module_insert it would "hook" on the function hook_insert. To prevent that I can rename my function to _my_module_insert.
ps
The way hooks works in Drupal it's possible to implement a hook by mistake, which is very bad.
Drupal, and using underscore:
In a general way the underscore is to simple mark the fact that a function would probably only be called by a related parent function...
function mymodule_tool($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...
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.
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.
They are called "magic methods".
I know there are a couple of similar questions here in StackOverflow like this question.
Why is overriding method parameters a violation of strict standards in PHP?
For instance:
class Foo
{
public function bar(Array $bar){}
}
class Baz extends Foo
{
public function bar($bar) {}
}
Strict standards: Declaration of Baz::bar() should be compatible with
that of Foo::bar()
In other OOP programming languages you can. Why is it bad in PHP?
In OOP, SOLID stands for Single responsibility, Open-closed, Liskov substitution, Interface segregation and Dependency inversion.
Liskov substitution principle states that, in a computer program, if Bar is a subtype of Foo, then objects of type Foo may be replaced with objects of type Bar without altering any of the desirable properties of that program (correctness, task performed, etc.).
In strong-typed programming languages, when overriding a Foo method, if you change the signature in Bar, you are actually overloading since the original method and the new method are available with different signatures. Since PHP is weak typed, this is not possible to achieve, because the compiler can't know which of the methods you are actually calling. (hence the reason you can't have 2 methods with the same name, even if their signatures are different).
So, to avoid the violation of Liskov Substituition principle, a strict standard warning is issued, telling the programmer something might break due to the change of the method signature in the child class.
I know I am late to the party but the answers don't really spell out the actual problem.
The problem is PHP doesn't support function/method overloading. It would be difficult to support function overloading in an untyped language.
Hinting helps. but in PHP it is very limited. Not sure why. For example you cannot hint a variable is an int or Boolean yet array is fine. Go figure!
Other object orientated languages implement this using function overloading. Which is to say the signature of the function is obviously different.
So for example if the following was possible we would not have an issue
class Foo
{
public function bar(Array $bar){
echo "Foo::bar";
}
}
class Baz extends Foo
{
public function bar(int $bar) {
echo "Baz::bar";
}
}
$foo = new Baz();
$bar = new Baz();
$ar = array();
$i = 100;
$foo->bar($ar);
$bar->bar((int)$i);
would output
Foo::bar
Baz::bar
Of course when it came to constructors the php developers realised they have to implement it, Like it or not! So they simply suppress the error or not raise it in the first case.
Which is silly.
An acquaintance once said PHP implemented objects only as a way of implementing namespaces. Now I am not quite that critical but some of the decisions taken do tend to support that theory.
I always have maximum warnings turned on when developing code, I never let a warning go by without understanding what it means and what the implications are. Personally I don't care for this warning. I know what I want to do and PHP doesn't do it right. I came here looking for a way to selectively suppress it. I haven't found a way yet.
So I will trap this warning and suppress it myself. Shame I need to do this. but I am strict about STRICT.
You can override parameters, but the signature should match. If you had put Array out in front of $bar, there would be no problem.
For example, if you had added an additional parameter, there would be no problem, provided the first parameter had the same type hinting. This is good practice in any language.
Because you declared on Foo that $bar should be of type array, while in the extending Bar, $bar's type isn't declared.
This isn't an error, it's a warning. You should make the method definition compatible with the original, base class. You can, however, safely ignore it if you know what you're doing (and only if you know what you're doing!!!)
I was wondering if there is a way to force phpDocumentor to print out the potential methods you could use for getting and setting when you do them dynamically with a __call().
In the case of my simple getter, I would want it to cycle through all private variables and just append get to them (and uppercase the first letter, of course).
See the phpDocumentor reference on #method.
I have some code I'm working with that was written by the guy before me and I'm trying to look it over and get a feel for the system and how it all works. I am also fairly new to PHP, so I have a few questions for those willing and able to provide.
The basic breakdown of the code in question is this:
$__CMS_CONN__ = new PDO(DB_DSN, DB_USER, DB_PASS);
Record::connection($__CMS_CONN__);
First question, I know the double underscore makes it magic, but I haven't been able to find anywhere exactly what properties that extends to it, beyond that it behaves like a constant, kind of. So what does that mean?
class Record
{
public static $__CONN__ = false;
final public static function connection($connection)
{
self::$__CONN__ = $connection;
}
}
Second, these two pieces go together. They are each in separate files. From what I've read, static variables can be referenced in the same way as static functions, so couldn't you just call the variable and set it directly instead of using the function?
I get the feeling it's more involved than I am aware, but I need to start somewhere.
This isn't a magic variable. The person who wrote that shouldn't really use double underscores for variable names like that because it can cause confusion.
This is just a static property on a class. Which means it is shared between instances of that class (in the same php request).
Have a look at the docs for static properties if you're unsure on how these work.
There are several predefined "magic constants" that use this naming style. However, I don't think the underscores mean anything special (as far as the language is concerned); i.e. defining your own variable like this won't bestow it any magical properties. It may be part of the previous programmer's naming convention, and if so, it's probably ill-advised.
Setting a property via a function can, in many circumstances, make the "client" code more resilient to changes in the implementation of the class. All implementation details can be hidden inside the method (known as a "setter"). However, there are strong feelings about whether this is a good idea or not (I, for one, am not a big fan).
Two underscores do not make a variable magic.
It's better to use getters/setters than to access class properties directly.
The PHP manual has this to say on naming variables (and other symbols) with underscores:
PHP reserves all symbols starting with __ as magical. It is recommended that you do not create symbols starting with __ in PHP unless you want to use documented magical functionality.
Pay particular attention to the use of the words "reserves" and "documented". They mean double underscores shouldn't be used for user-defined symbols as it may lead to future conflicts, and that unless the symbol is explicitly mentioned in the manual as being magic, it's mundane.