I have a class like this.
<?php
namespace test;
class Test
{
public static function static1(){}
public static function static1(){}
...
}
And autoload use psr-4.
when is the static function load in memory ?
load with out use(include) ? I don't think it will do this.
use test/Test(include php file) ?
call Test.static1(); ?
In my option: static function is easy to use without new(of course, they don't have private data), but i afraid it's load more memory and make performance degradation.
Disclaimer: What you're asking/saying doesn't make a lot of sense to me. You need to research and correct your terminology and learn more about static methods or properties. I believe when you're referring to private data, you're actually referring to "instance properties".
Static methods would use no more memory than an instance method, not sure where you came up with that idea. The code of the class is loaded into memory by the compiler when it is included. Except for their definition (compiled code), methods or functions do not use memory. The amount of memory consumed when a method is run depends entirely on what the method is doing.
Methods have no private properties, classes have private properties, and a static method can access private properties.
If your goal is to have a property persist across multiple instances, you can access a static property from within an instance method:
public function getData() {
// self::$data or static::$data represents a static property $data
return self::$data;
}
If your goal is to only have one instance of a class exist at any time, you can look up the Singleton pattern.
If anything, static methods and properties can be more efficient than instance counterparts. One of the problems with static methods is they are less testable, you can do your own research on why you may want to avoid static methods, but performance is not likely one of the reasons.
Related
I'm using OOP aproach in php.I'm just learning though. Each time I need to access a method in a class I instantiate a object.So I have quite a number of objects created in my project to do each task.Is there a way where I can only create one object and share throughout the project to do multiple method for different task?
Also in my class, I declared the variable first and then use them like $this->property = $assign_variable.Will declaring variable earlier would consume memory much?
I'm just concerned to approach the right and effective way of instantiating object and declaring class in OOP. Can anyone suggest please?
Having multiple instances of an object consumes more memory (much is relative), as every attribute of an object needs to have allocated memory. If you have an object that consumes, lets say, x bytes of memory for its attributes, then you will need n*x bytes of memory if you instantiate n objects in total (There is also a neglactable amount of memory used which needs to be used for the code, but the amount is constant). In normal use that shouldn't be a problem though (i.e. if you don't have an unusual huge amount of objects).
If you need only one instance of a class through the whole program, I'd suggest you to use the Singleton design pattern 1].
Here is an example:
class Singleton {
// This is where the one and only instance is stored
private static $instance = null;
private __construct() {
// Private constructor so the class can't be initialized
}
// That's how you get the one and only instance
public static function getInstance() {
if (Singleton::$instance === null) {
Singleton::$instance = new Singleton();
}
return Singleton::$instance;
}
public function doSomething() {
// here you can do whatever you need to do with the one and only object of this class
}
}
You can then use it very conveniently like this:
Singleton::getInstance()->doSomething();
So you are basically just storing the address of the object in one location, namely Singleton::$instance.
Another option for you could be to use static methods. It is defined like above in the Singleton pattern:
class StaticExample {
// ...
public static function doSomething() {
// your code
}
}
And can be accessed with StaticExample::doSomething();
I also want to note that usually, you don't have much classes in a project which implements the Singleton design pattern or use the static keyword very often. If you want to use a lot of singletons or see yourself needing a lot of statics, you probably got something wrong and should post an example of your code on another site like Programmers Stack Exchange.
1] Singleton design pattern on Wikipedia
I am a junior PHP programmer. I still have a lot to learn. That's why I ask this question. In a class you have a public function which you can call it from outside that class. Sometimes you have a private function which you can call several times in that class where the private function resides, for reusable purpose. I like to set the private function to static and I call that function with:
self::privateFunctionName();
By using self it reminds me that this private function resides in that class. if I use $this->privateFunctionName() for non-static function, it could be in the superclass/base class or in that subclass itself. That is why I like to use static private function. In a professional point of view, is it a good idea to use static private function instead of non-static? Is there any disadvantage that a professional programmer like you prefers to avoid the static function?
Only using self::... must not mean the method is static. parent:: and self:: work as well for non-static methods. You can find this in the PHP manual - Scope Resolution Operator (::) and I add some exemplary code excerpt at the end of the answer.
You perhaps might want to read through all answers of this earlier question:
When to use self over $this?
In total you will get there more details then my short description in this answer.
You might have been confused by the scope-resolution-operator :: which is used by those. I had a similar understanding problem grasping that.
However, do not just choose to use static methods for such a limited reason. Those static class methods should only be used in very limited and narrowed situations. As a rule of thumb:
"Do not use static class methods."
If you like to start with object oriented programming, just use normal object methods.
Here is an excerpt from existing code that shows that self:: as well as parent:: are used with standard (non-static) methods:
<?php
...
/**
* Class XMLElementIterator
*
* Iterate over XMLReader element nodes
*/
class XMLElementIterator extends XMLReaderIterator
{
private $index;
private $name;
private $didRewind;
/**
* #param XMLReader $reader
* #param null|string $name element name, leave empty or use '*' for all elements
*/
public function __construct(XMLReader $reader, $name = null)
{
parent::__construct($reader);
$this->setName($name);
}
/**
* #return void
*/
public function rewind()
{
parent::rewind();
$this->ensureCurrentElementState();
$this->didRewind = true;
$this->index = 0;
}
/**
* #return XMLReaderNode|null
*/
public function current()
{
$this->didRewind || self::rewind();
$this->ensureCurrentElementState();
return self::valid() ? new XMLReaderNode($this->reader) : null;
}
...
self:: does not in fact mean that the method is part of the same class, it may as well have been inherited from a parent class!
You should not use the semantics of static method calls to differentiate "internal" and "external" methods. There's no real point to it anyway, and you're just abusing language features for something they weren't meant for. Maybe let that be a primary lesson: don't try to invent clever new ways of using language features. Just don't.
You should view methods as small, self contained black boxes. You don't need to know and don't want to know what they do. All you know is that when you call method foo with parameter $bar, x will happen or it will return y. You don't care how this happens, just that it does because that's what the method is supposed to do.
As such, static and non-static methods convey a different use with different limitations. static methods are supposed to be called when you don't have an object, for example as alternative constructor methods (e.g. DateTime::createFromFormat).
Further, restricting a method to being static means it has no access to object instance data, which may limit you in the future. As your project evolves, you may find that your method now needs to take into account some additional data from the object to do its job. If you declared it as non-static from the beginning, all it takes is a little modification to the method itself; to the outside world it still does its job the same way (input → output). However, if you declared it as static and suddenly find yourself needing to make it non-static, you have to change a lot more code than just that one method.
Bottom line: if your method is not supposed to be exposed publicly because it's nobody's business to call it except for your own class, make it private. If the method needs to be static because it must work without object context, make it static. If it fulfils both requirements, make it private static. Otherwise, don't.
Well basically a "private static" function is a construct which is totally nonsense because it cannot be called from the outside.
There is no real difference between $this-> and using self:: expect the fact that it can be called from the outside without a object and its the same amount of work for the CPU to call the function, no matter in what namespace/class this function is located.
However the fact that a private function can only be called within the same class you always have an object and the "static" modifier is somewhat superflous here because it makes no difference.
In this cases I always like to say: do what you like its just a matter of your personal style but dont switch arround, keep it that way to develop and use the standard you feel comfortable with.
In some cases there is just "another" way and a "professional" way does not exist at all.
The trend often makes the one or the other method to become popular over time.
I understand that static means that an object doesn't need to be instantiated for that property/method to be available. I also understand how this applies to private properties and methods and public methods. What I'm trying to understand is what static private function gains you. For example:
class Beer {
static private $beertype = "IPA";
private function getBeerType() {
return self::$beertype;
}
static public function BeerInfo() {
return self::getBeerType();
}
}
print Beer::BeerInfo() . "\n";
The private method getBeerType() executes just fine without an instantiated object as long as it's being called from a static public method. If a static public method has access to all private methods (static and non-static), what's the benefit of declaring a method static private?
With strict error reporting turned on, I do get the warning that I should make getBeerType() static, although it still lets me run the code. And I did a little research and it seems like other languages (Java) will force you to declare a private method as static when called by a static public method. Looks like PHP lets you get away with this. Is there a way to force it to throw an error and not execute?
A static private method provides a way to hide static code from outside the class. This can be useful if several different methods (static or not) need to use it, i.e. code-reuse.
Static methods and static variables, sometimes called class methods and class variables, are a way of putting code and data into a kind of namespace. You could also think of class variables as variables attached to the class itself, of which there is (by definition) exactly one, instead of to instances of that class, of which there may be zero, one or many. Class methods and class variables can be useful in working with attributes that not just remain same in all instances, but actually be the same.
An example of a class variable is a database handler in an ORM entity object. All instances are their own object, but they all need access to the same database handler for loading and saving themselves.
Private versus public is a completely separate quality, which is I suspect what you're stumbling over. A private method cannot be called and private variables cannot be accessed from code outside the class. Private methods are usually used to implement "internal" logic on the object that must not be accessible from outside the object. This restriction can be needed by instance methods as well as class methods.
An example of a private class method could be in a factory method. There might be three factory calls for creating an object which might differ in parameters being supplied. Yet the bulk of the operation is the same. So it goes into a private static method that the non-private factory methods call.
I understand static means that an object doesn't need to be instantiated for that property/method to be available.
Everything static just exists. Globally.
I also understand how this applies to public properties and methods and public methods
Are you sure you have understood that it creates a global variable and a standard global function?
What I'm trying to understand is what static private function gains you.
The private is just a specifier of visibilityDocs. So that gains you visibility control.
Is it useful? Depends on the use-case.
it's for preventing OTHERS from consuming it.
Example, you have a Logger static object, then you have two public static methods LogOk and LogError and both benefeit from an "internal" method Log but you don't want the consumers of that class to be able to call Log directly.
You can call Logger::LogOk( "All right." ); but you cannot call Logger::Log( "abc" ); if Log is private.
You you can internally always make use of it from the same class.
Although the code works, it throws a Strict standards error:
Strict standards: Non-static method Beer::getBeerType() should not be
called statically
So, here you get the use of the private static.
Simply said you can declare a private static function if you have a repeated operation in some of the public static functions in the class.
Naturally if you are an inexperienced programmer or new to the OOP putting limitations to your code seem strange. But strict declarations like this will make your code cleaner and easier to maintain.
In large projects and complex classes you can appreciate to know exactly what to expect from a function and exactly how you can use it.
Here is a good read: Single responsibility principle and
God Object
Here's the rule and the best answer,
static methods cannot access non-static variables and methods, since these require an instance of the class. Don't worry about the warning, the rule is set and it will break your code in the future once it's fully enforced. That is why
static public function BeerInfo() {
return self::getBeerType()
is wrong,
you have to declare getBeerType as static.
In your example, you can simplify this by doing the following.
static private $beertype = "IPA";
static public function BeerInfo() {
return self::$beertype;
}
'static' purely means resident in a single region of memory. If you are memory conscious, static implementations are a good strategy.
When you use a public static function, chances are, most of the time, that you don't want to deal with an instance of that class, but want to re-use pre-existing functionality from within that class. Leveraging private static functions is the way to do that without instances.
However, you could have a public static function which accepts an argument which is an instance of said class, e.g.
static public function doSomething(Beer &$ref) {
$ref->instanceLevelFunction(...);
}
What is better to use in this context, static methods, or simple public method and call them always like this: $request = new Request();
if($request->isPostRequest()){ do smth }
ofcourse its easier to use static, but what is more properly to use?
Class Request {
public static function isSecureConnection() {}
public static function isPostRequest() {}
public static function isAjaxRequest() {}
...etc
}
If each Request is a genuine entity, then it would be better to use non-static members. But if it's not and methods are used in general, like Sinus function in math, then they'd be better to be static.
Overall it'd be better to declare static functions in a class that is just consisted of functions and no data members.
You should always create a class like if it was to be used on a non-static environment.
Then you can use that as a Singleton with lazy-instantiation. Or even as a Static class instantiation. Or even as a Standalone instance object. You decide later what to do with it.
If you start by declaring all members as static you are basically just covering a bunch of Global variables inside a glorified namespace known as a Class. You also will statically allocate the memory used by that class even if you don't call it or use it in your code.
So, just write as a Class, then you decide what to do with it. Static/Non-Static. Singleton/Instance. Factory Pattern or not. Memory Allocator X/DLL bound or whatnot.
The only exception is static members used for book-keeping in behalf of the Object Instances; things like reference counting, caches and things like that. That is the good thing about static/non-static, you can mix and match for some clever behaviors.
What if later you wanted another Request? Or what would happen if you can create more than one because you are in a multithreaded environment? Things will get really strange once you go that route with statics.
It looks like you are handling one particular request.
Now this insinuates you should make it a singleton, and/or use static functions.
Reason:
There is only one request, all the state is defined by the environment delivered to the process. The class methods are just helper functions, and you want to be able to use them without class instance.
On the other hand, you would rarely use static functions with classes that represent one of many, for example one user of many, one question of many.
Declaring class properties or methods as static makes them accessible without needing an instantiation of the class. A property declared as static can not be accessed with an instantiated class object (though a static method can).
Example:
<?php
class Foo {
public static function aStaticMethod() {
// ...
}
}
Foo::aStaticMethod();
$classname = 'Foo';
$classname::aStaticMethod(); // As of PHP 5.3.0
?>
See the reference of Static Keyword from php.net.
If you can, use static methods as a default. static methods run quicker than their non-static counterparts.
According to the PHP manual, a class like this:
abstract class Example {}
cannot be instantiated. If I need a class without instance, e.g. for a registry pattern:
class Registry {}
// and later:
echo Registry::$someValue;
would it be considered good style to simply declare the class as abstract? If not, what are the advantages of hiding the constructor as protected method compared to an abstract class?
Rationale for asking: As far as I see it, it could a bit of feature abuse, since the manual refers to abstract classes more as like blueprints for later classes with instantiation possibility.
Update: First of all, thanks for all the answers! But many answers sound quite alike: 'You cannot instantiate an abstract class, but for a registry, why not using a singleton pattern?'
Unfortunately, that was more or less exactly a repeat of my question. What is the advantage of using a singleton pattern (a.k.a. hiding __construct()) compared to just declaring it abstract and not having to worry about that? (Like, e.g., it is a strong connotation between developers, that abstract classes are not actually used or so.)
If your class is not meant to define some super-type, it should not be declared as abstract, I'd say.
In your case, I would rather go with a class :
That defines __construct and __clone as private methods
so the class cannot be instanciated from outside
And, this way, your class could create an instance of itself
See the Singleton design pattern, about that, btw
Now, why use a Singleton, and not only static methods ? I suppose that, at least a couple of reasons can be valid :
Using a singleton means using an instance of the class ; makes it easier to transform a non-singleton class to a singleton one : only have to make __construct and __clone private, and add some getInstance method.
Using a singleton also means you have access to everything you can use with a normal instance : $this, properties, ...
Oh, a third one (not sure about that, but might have its importance) : with PHP < 5.3, you have less possibilities with static methods/data :
__callStatic has only been introduced in PHP 5.3
There is no __getStatic, __setStatic, ...
Same for a couple of other Magic methods !
Late Static Binding has only been added with PHP 5.3 ; and not having it often makes it harder, when working with static methods/classes ; especially when using inheritance.
This being said, yes, some code like this :
abstract class MyClass {
protected static $data;
public static function setA($a) {
self::$data['a'] = $a;
}
public static function getA() {
return self::$data['a'];
}
}
MyClass::setA(20);
var_dump(MyClass::getA());
Will work... But it doesn't feel quite natural... and this is a very simple example (see what I said earlier with Late Static Binding, and magic methods).
What you describe is permitted by the PHP language, but it's not the intended usage of an abstract class. I wouldn't use static methods of an abstract class.
Here's the downside of doing that: Another developer could extend your abstract class and then instantiate an object, which is what you want to avoid. Example:
class MyRegistry extends AbstractRegistry { }
$reg = new MyRegistry();
True, you only need to worry about this if you're handing off your abstract class to another developer who won't comply with your intended usage, but that's why you would make the class a singleton too. An uncooperative developer can override a private constructor:
class Registry
{
private function __construct() { }
}
class MyRegistry extends Registry
{
public function __construct() { } // change private to public
}
If you were using this class yourself, you would simply remember not to instantiate the class. Then you wouldn't need either mechanism to prevent it. So since you're designing this to be used by others, you need some way to prevent those people from circumventing your intended usage.
So I offer these two possible alternatives:
Stick with the singleton pattern and make sure the constructor is also final so no one can extend your class and change the constructor to non-private:
class Registry
{
private final function __construct() {
}
}
Make your Registry support both static and object usage:
class Registry
{
protected static $reg = null;
public static function getInstance() {
if (self::$reg === null) {
self::$reg = new Registry();
}
return self::$reg;
}
}
Then you can call Registry::getInstance() statically, or you can call new Registry() if you want an object instance.
Then you can do nifty things like store a new registry instance inside your global registry! :-)
I implemented this as part of Zend Framework, in Zend_Registry
As other guys said, you cannot instantiate an abstract class. You could use static methods in your class to prevent instantiating, but I'm not really a fan of doing so unless I have a proper reason.
I might be little bit off-topic now, but in your example you said you wanted this for Registry pattern class. What is the reason you don't want to instantiate it? Wouldn't it better to create an instance of Registry for each registry you want to use?
Something like:
class Registry {
private $_objects = array( );
public function set( $name, $object ) {
$this->_objects[ $name ] = $object;
}
public function get( $name ) {
return $this->_objects[ $name ];
}
}
I wouldn't even use Singleton in this case.
Setting a class to abstract that only defines static properties/methods won't have a real effect. You can extend the class, instantiate it, and call a method on it and it would change the static class properties. Obviously very confusing.
Abstract is also misleading. Abstract is ment to define an class that implements some functionality, but needs more behaviour (added via inheritance) to function properly. On top of that it's usually a feature that shouldn't be used with static at all. You are practically inviting programmers to use it wrong.
Short answer: A private constructor would be more expressive and fail safe.
There are patterns in OO that are common and well-recognized. Using abstract in an unconventional way may cause confusion (sorry, my some examples are in Java instead of PHP):
abstract class - a class meant to conceptualize a common ancestor, but of which actual instances are not meant to exist (e.g. shape is an abstract superclass for rectangle and triangle).
Commonly implemented by:
use abstract modifier on class to prevent direct instantiation, but allow deriving from the class
utility class - a class that does not represent an object in the solution space, but rather is a collection of useful static operations/methods, e.g. Math class in Java.
Commonly implemented by:
make class non-derivable, e.g. Java uses the final modifier on class, and
prevent direct instantiation - provide no constructors and hide or disable any implicit or default constructors (and copy constructors)
singleton class - a class that does represent an object in the solution space, but whose instantiation is controlled or limited, often to insure there is only one instance.
Commonly implemented by:
make class non-derivable, e.g. Java uses the final modifier on class, and
prevent direct instantiation - provide no constructors and hide or disable any implicit or default constructors (and copy constructors), and
provide a specific means to acquire an instance - a static method (often getInstance()) that returns the only instance or one of the limited number of instances
abstract really is meant to indicate a "blueprint", as you call it, for class inheritance.
Registries generally follow a singleton pattern, which means they it would instantiate itself in a private variable. Defining it as abstract would prevent this from working.
I wouldnt use an abstract class. Id use something more akin to a singleton with a protected/private constructor as you suggest. There should be very few static properties other than $instance which is the actual registry instance. Recently ive become a fan of Zend Frameworks typical pattern which is something like this:
class MyRegistry {
protected static $instance = null;
public function __construct($options = null)
{
}
public static function setInstance(MyRegistry $instance)
{
self::$instance = $instance;
}
public static function getInstance()
{
if(null === self::$instance) {
self::$instance = new self;
}
return self::$instance;
}
}
This way you get a singleton essentially but you can inject a configured instance to use. This is handy for testing purposes and inheritance.
The purpose of an abstract class is to define methods that are 1) meaningful to other classes and 2) not meaningful when not in the context of one of those classes.
To paraphase some of the php docs, imagine you are connecting to a database. Connecting to a database doesn't make much sense unless you have a particular kind of database to connect to. Yet connecting is something you will want to do regardless of the kind of database. Therefore, connecting can be defined in an abstract database class and inherited, and made meaningful by, say, a MYSQL class.
From your requirements, it sounds like you don't intend to do this but instead simply require a class without an instance. Whilst you could use an abstract class to enforce this behaviour, this seems hacky to me because it abuses the purpose of abstract classes. If I encounter an abstract class, I should be able to reasonably expect that this will have some abstract methods, for example, but your class will have none.
Therefore, a singleton seems like a better option.
However, if the reason you wish to have a class without an instance is simply so that you can call it anywhere then why do you even have a class at all? Why not just load every variable as a global and then you can just call it directly rather than through the class?
I think the best way to do this is to instantiate the class and then pass it around with dependency injection. If you are too lazy to do that (and fair enough if you are! Its your code, not mine.) then don't bother with the class at all.
UPDATE: It seems like you are conflicted between 2 needs: The need to do things quickly and the need to do things the right way. If you don't care about carrying a ton of global variables for the sake of saving yourself time, you will assumedly prefer using abstract over a singleton because it involves less typing. Pick which need is more important to you and stick with it.
The right way here is definitely not to use a Singleton or an abstract class and instead use dependency injection. The fast way is to have a ton of globals or an abstract class.
From my understanding, a class without instance is something you shouldn't be using in an OOP program, because the whole (and sole) purpose of classes is to serve as blueprints for new objects. The only difference between Registry::$someValue and $GLOBALS['Registry_someValue'] is that the former looks 'fancier', but neither way is really object-oriented.
So, to answer your question, you don't want a "singleton class", you want a singleton object, optionally equipped with a factory method:
class Registry
{
static $obj = null;
protected function __construct() {
...
}
static function object() {
return self::$obj ? self::$obj : self::$obj = new self;
}
}
...
Registry::object()->someValue;
Clearly abstract won't work here.
I would say it's a matter of coding habbits. When you think of an abstract class it is usually something you need to subclass in order to use. So declaring your class abstract is counter-intuitive.
Other than that is it just a matter of using self::$somevar in your methods if you make it abstract, rather than $this->somevar if you implement it as a singleton.