<?php
class A{
//many properties
protected $myProperty1;
protected $myProperty2;
protected $myProperty3;
public function __construct(){
$this->myProperty1='some value';
$this->myProperty2='some value';
$this->myProperty3='some value';
}
public function getProperty1(){
return $this->myProperty1;
}
public function getProperty2(){
return $this->myProperty2;
}
public function getProperty3(){
return $this->myProperty3;
}
//edited: I added some setters, meaning that the object returned from the functions may already have these properties altered
public function setProperty1($p){
$this->myProperty1=$p;
}
public function setProperty2($p){
$this->myProperty2=$p;
}
public function setProperty3($p){
$this->myProperty3=$p;
}
}
class B extends A{
private $myProperty4;
public function __construct(A $a){
$this=$a; //this line has error,it says $this cannot be re-assigned
$this->myProperty4='some value';
}
public function getProperty4(){
return $this->myProperty4;
}
}
//$a = new A();
$a = someClass::getAById(1234); //edited: $a is returned by a function (I cannot modify it)
$b= new B($a); //error
?>
I'd like to create a B's object by passing an A's object to B's constructor, as you can see, I cannot re-assign the $this variable. I am not allowed to modify class A, when there are many properties in A, it'd be tedious for me to do things like this in B's constructor:
public function __construct(A $a){
parent::__construct();
$this->myProperty1=$a->getProperty1();
$this->myProperty2=$a->getProperty2();
$this->myProperty3=$a->getProperty3();
$this->myProperty4='some value';
}
My question is that, how can I safely create an object of class B using an A's object with minimal amount of coding?
class A
{
public $property = 'Foobar';
}
class B extends A
{
public function __construct()
{
echo $this->property; // Foobar
}
}
Am I missing something? It sounds like you're trying to force OOP to do something it's not intended to do, or you're having trouble understanding inheritance.
Every public or protected method and property from class A is available in class B. Either by directly referencing it (as in my example) or by using the parent:: syntax.
EDIT
(Author clarified question)
If class A's properties are accessible, you could use something like the following to copy them down to class B
class B
{
public function __construct()
{
$a = new A(); // Or however A is instantiated
foreach(get_object_vars($a) as $key => $value)
{
$this->$key = $value;
}
}
}
Since B extends A, why not just create B to begin with? If you need to initialize some extra properties, you can over-ride the constructor like this:
class B extends A {
public function __construct(){
parent::__construct(); //calls A's constructor
$this->Bproperty='somevalue';
}
}
If that's not good enough, then you might want to look at Reflection.
Related
I have 2 classes declared like in the example below.
class A{
protected $process;
public function __construct() {
......
$this->process=new B();
}
public function do_something(){
....
}
}
class B{
// content not important
// I need to call do_something from class A
}
My question is, how can I call from class B the method do_something() from class A? Is it possible?
From your example it is impossible for instance of B to know that it is instantiated and stored by an instance of class A. You need to create that connection explicitly in some way.
I didn't think this would even work, but apparently you can pass instance of A to B before A is even done with its constructor:
class A {
protected $process;
public function __construct() {
$this->process = new B( $this );
}
public function do_something() {
var_dump( 'do_something' );
}
public function test() {
$this->process->test();
}
}
class B {
public function __construct( A $a ) {
$this->a = $a;
}
public function test() {
$this->a->do_something();
}
}
$a = new A();
$a->test(); // do_something
It's hard to give an advice on what the best approach for your particular case would be, as we don't know what either A or B does.
There's a few ways to achieve this. One way would be to make B and extension of A - thereby allowing all methods of the class A to be callable on the object B. Another way is to create a new object of A inside B and call that method. Or you can pass
Here's an example where B is extended from A. By doing this, all properties and methods of A can be called on B, unless overwritten in B.
class A {
public function doSomething(){
echo "doSomething() called in A";
}
}
class B extends A {
public function someMethod() {
$this->doSomething();
}
}
$b = new B();
$b->someMethod();
The above would output doSomething() called in A.
Or, you can create an object A and call that method inside B.
class B {
public function someMethod() {
$a = new A();
$a->do_something();
}
}
$b = new B();
$b->someMethod();
After reading all the answers and doing some research i think that the best method for me was the use of Traits
"Traits are a mechanism for code reuse in single inheritance languages such as PHP. A Trait is intended to reduce some limitations of single inheritance by enabling a developer to reuse sets of methods freely in several independent classes living in different class hierarchies."
So i declared a Trait with the method do_something and call that method from Both class A and Class B
Thanks
Is there any way to define abstract class properties in PHP?
abstract class Foo_Abstract {
abstract public $tablename;
}
class Foo extends Foo_Abstract {
//Foo must 'implement' $property
public $tablename = 'users';
}
There is no such thing as defining a property.
You can only declare properties because they are containers of data reserved in memory on initialization.
A function on the other hand can be declared (types, name, parameters) without being defined (function body missing) and thus, can be made abstract.
"Abstract" only indicates that something was declared but not defined and therefore before using it, you need to define it or it becomes useless.
No, there is no way to enforce that with the compiler, you'd have to use run-time checks (say, in the constructor) for the $tablename variable, e.g.:
class Foo_Abstract {
public final function __construct(/*whatever*/) {
if(!isset($this->tablename))
throw new LogicException(get_class($this) . ' must have a $tablename');
}
}
To enforce this for all derived classes of Foo_Abstract you would have to make Foo_Abstract's constructor final, preventing overriding.
You could declare an abstract getter instead:
abstract class Foo_Abstract {
abstract public function get_tablename();
}
class Foo extends Foo_Abstract {
protected $tablename = 'tablename';
public function get_tablename() {
return $this->tablename;
}
}
Depending on the context of the property, if I want to force declaration of an abstract class property in an extended class, I like to use a constant with the static keyword for the property in the abstract object constructor or setter/getter methods. You can optionally use final to prevent the method from being overridden in extended classes.
Example: https://3v4l.org/WH5Xl
abstract class AbstractFoo
{
public $bar;
final public function __construct()
{
$this->bar = static::BAR;
}
}
class Foo extends AbstractFoo
{
//const BAR = 'foobar'; //uncomment to prevent exception
}
$foo = new Foo();
//Fatal Error: Undefined class constant 'BAR'
However, the extended class overrides the parent class properties and methods if redefined.
For example; if a property is declared as protected in the parent and redefined as public in the extended class, the resulting property is public. Otherwise, if the property is declared private in the parent it will remain private and not available to the extended class.
http://www.php.net//manual/en/language.oop5.static.php
As stated above, there is no such exact definition.
I, however, use this simple workaround to force the child class to define the "abstract" property:
abstract class Father
{
public $name;
abstract protected function setName(); // now every child class must declare this
// function and thus declare the property
public function __construct()
{
$this->setName();
}
}
class Son extends Father
{
protected function setName()
{
$this->name = "son";
}
function __construct(){
parent::__construct();
}
}
The need for abstract properties can indicate design problems. While many of answers implement kind of Template method pattern and it works, it always looks kind of strange.
Let's take a look at the original example:
abstract class Foo_Abstract {
abstract public $tablename;
}
class Foo extends Foo_Abstract {
//Foo must 'implement' $property
public $tablename = 'users';
}
To mark something abstract is to indicate it a must-have thing. Well, a must-have value (in this case) is a required dependency, so it should be passed to the constructor during instantiation:
class Table
{
private $name;
public function __construct(string $name)
{
$this->name = $name;
}
public function name(): string
{
return $this->name;
}
}
Then if you actually want a more concrete named class you can inherit like so:
final class UsersTable extends Table
{
public function __construct()
{
parent::__construct('users');
}
}
This can be useful if you use DI container and have to pass different tables for different objects.
I've asked myself the same question today, and I'd like to add my two cents.
The reason we would like abstract properties is to make sure that subclasses define them and throw exceptions when they don't. In my specific case, I needed something that could work with statically.
Ideally I would like something like this:
abstract class A {
abstract protected static $prop;
}
class B extends A {
protected static $prop = 'B prop'; // $prop defined, B loads successfully
}
class C extends A {
// throws an exception when loading C for the first time because $prop
// is not defined.
}
I ended up with this implementation
abstract class A
{
// no $prop definition in A!
public static final function getProp()
{
return static::$prop;
}
}
class B extends A
{
protected static $prop = 'B prop';
}
class C extends A
{
}
As you can see, in A I don't define $prop, but I use it in a static getter. Therefore, the following code works
B::getProp();
// => 'B prop'
$b = new B();
$b->getProp();
// => 'B prop'
In C, on the other hand, I don't define $prop, so I get exceptions:
C::getProp();
// => Exception!
$c = new C();
$c->getProp();
// => Exception!
I must call the getProp() method to get the exception and I can't get it on class loading, but it is quite close to the desired behavior, at least in my case.
I define getProp() as final to avoid that some smart guy (aka myself in 6 months) is tempted to do
class D extends A {
public static function getProp() {
// really smart
}
}
D::getProp();
// => no exception...
As you could have found out by just testing your code:
Fatal error: Properties cannot be declared abstract in ... on line 3
No, there is not. Properties cannot be declared abstract in PHP.
However you can implement a getter/setter function abstract, this might be what you're looking for.
Properties aren't implemented (especially public properties), they just exist (or not):
$foo = new Foo;
$foo->publicProperty = 'Bar';
PHP 7 makes it quite a bit easier for making abstract "properties". Just as above, you will make them by creating abstract functions, but with PHP 7 you can define the return type for that function, which makes things a lot easier when you're building a base class that anyone can extend.
<?php
abstract class FooBase {
abstract public function FooProp(): string;
abstract public function BarProp(): BarClass;
public function foo() {
return $this->FooProp();
}
public function bar() {
return $this->BarProp()->name();
}
}
class BarClass {
public function name() {
return 'Bar!';
}
}
class FooClass extends FooBase {
public function FooProp(): string {
return 'Foo!';
}
public function BarProp(): BarClass {
// This would not work:
// return 'not working';
// But this will!
return new BarClass();
}
}
$test = new FooClass();
echo $test->foo() . PHP_EOL;
echo $test->bar() . PHP_EOL;
if tablename value will never change during the object's lifetime, following will be a simple yet safe implementation.
abstract class Foo_Abstract {
abstract protected function getTablename();
public function showTableName()
{
echo 'my table name is '.$this->getTablename();
}
}
class Foo extends Foo_Abstract {
//Foo must 'implement' getTablename()
protected function getTablename()
{
return 'users';
}
}
the key here is that the string value 'users' is specified and returned directly in getTablename() in child class implementation. The function mimics a "readonly" property.
This is fairly similar to a solution posted earlier on which uses an additional variable. I also like Marco's solution though it can be a bit more complicated.
Just define the property in the base class without assigning it a (default) value.
Getting the property value without redefining it with a default value or assigning it a value will throw an Error.
<?php
class Base {
protected string $name;
public function i_am() : string {
return $this->name;
}
}
class Wrong extends Base {
...
}
class Good extends Base {
protected string $name = 'Somebody';
}
$test = new Good();
echo $test->i_am(), '<br>'; // Will show "Nobody"
$test = new Wrong();
echo $test->i_am(), '<br>'; // Will throw an Error:
// Error: Typed property Base::$name must not be accessed before initialization in ....
?>
You can define a static property in an abstract class.
<?php
abstract class Foo {
private static $bar = "1234";
public static function func() {
echo self::$bar;
}
}
Foo::func(); // It will be printed 1234
Too late to answer the question, but you may use the difference between self and static as follows
<?php
class A { // Base Class
protected static $name = 'ClassA';
public static function getSelfName() {
return self::$name;
}
public static function getStaticName() {
return static::$name;
}
}
class B extends A {
protected static $name = 'ClassB';
}
echo A::getSelfName(); // ClassA
echo A::getStaticName(); // ClassA
echo B::getSelfName(); // ClassA
echo B::getStaticName(); // ClassB
Is there any way to define abstract class properties in PHP?
abstract class Foo_Abstract {
abstract public $tablename;
}
class Foo extends Foo_Abstract {
//Foo must 'implement' $property
public $tablename = 'users';
}
There is no such thing as defining a property.
You can only declare properties because they are containers of data reserved in memory on initialization.
A function on the other hand can be declared (types, name, parameters) without being defined (function body missing) and thus, can be made abstract.
"Abstract" only indicates that something was declared but not defined and therefore before using it, you need to define it or it becomes useless.
No, there is no way to enforce that with the compiler, you'd have to use run-time checks (say, in the constructor) for the $tablename variable, e.g.:
class Foo_Abstract {
public final function __construct(/*whatever*/) {
if(!isset($this->tablename))
throw new LogicException(get_class($this) . ' must have a $tablename');
}
}
To enforce this for all derived classes of Foo_Abstract you would have to make Foo_Abstract's constructor final, preventing overriding.
You could declare an abstract getter instead:
abstract class Foo_Abstract {
abstract public function get_tablename();
}
class Foo extends Foo_Abstract {
protected $tablename = 'tablename';
public function get_tablename() {
return $this->tablename;
}
}
Depending on the context of the property, if I want to force declaration of an abstract class property in an extended class, I like to use a constant with the static keyword for the property in the abstract object constructor or setter/getter methods. You can optionally use final to prevent the method from being overridden in extended classes.
Example: https://3v4l.org/WH5Xl
abstract class AbstractFoo
{
public $bar;
final public function __construct()
{
$this->bar = static::BAR;
}
}
class Foo extends AbstractFoo
{
//const BAR = 'foobar'; //uncomment to prevent exception
}
$foo = new Foo();
//Fatal Error: Undefined class constant 'BAR'
However, the extended class overrides the parent class properties and methods if redefined.
For example; if a property is declared as protected in the parent and redefined as public in the extended class, the resulting property is public. Otherwise, if the property is declared private in the parent it will remain private and not available to the extended class.
http://www.php.net//manual/en/language.oop5.static.php
As stated above, there is no such exact definition.
I, however, use this simple workaround to force the child class to define the "abstract" property:
abstract class Father
{
public $name;
abstract protected function setName(); // now every child class must declare this
// function and thus declare the property
public function __construct()
{
$this->setName();
}
}
class Son extends Father
{
protected function setName()
{
$this->name = "son";
}
function __construct(){
parent::__construct();
}
}
The need for abstract properties can indicate design problems. While many of answers implement kind of Template method pattern and it works, it always looks kind of strange.
Let's take a look at the original example:
abstract class Foo_Abstract {
abstract public $tablename;
}
class Foo extends Foo_Abstract {
//Foo must 'implement' $property
public $tablename = 'users';
}
To mark something abstract is to indicate it a must-have thing. Well, a must-have value (in this case) is a required dependency, so it should be passed to the constructor during instantiation:
class Table
{
private $name;
public function __construct(string $name)
{
$this->name = $name;
}
public function name(): string
{
return $this->name;
}
}
Then if you actually want a more concrete named class you can inherit like so:
final class UsersTable extends Table
{
public function __construct()
{
parent::__construct('users');
}
}
This can be useful if you use DI container and have to pass different tables for different objects.
I've asked myself the same question today, and I'd like to add my two cents.
The reason we would like abstract properties is to make sure that subclasses define them and throw exceptions when they don't. In my specific case, I needed something that could work with statically.
Ideally I would like something like this:
abstract class A {
abstract protected static $prop;
}
class B extends A {
protected static $prop = 'B prop'; // $prop defined, B loads successfully
}
class C extends A {
// throws an exception when loading C for the first time because $prop
// is not defined.
}
I ended up with this implementation
abstract class A
{
// no $prop definition in A!
public static final function getProp()
{
return static::$prop;
}
}
class B extends A
{
protected static $prop = 'B prop';
}
class C extends A
{
}
As you can see, in A I don't define $prop, but I use it in a static getter. Therefore, the following code works
B::getProp();
// => 'B prop'
$b = new B();
$b->getProp();
// => 'B prop'
In C, on the other hand, I don't define $prop, so I get exceptions:
C::getProp();
// => Exception!
$c = new C();
$c->getProp();
// => Exception!
I must call the getProp() method to get the exception and I can't get it on class loading, but it is quite close to the desired behavior, at least in my case.
I define getProp() as final to avoid that some smart guy (aka myself in 6 months) is tempted to do
class D extends A {
public static function getProp() {
// really smart
}
}
D::getProp();
// => no exception...
As you could have found out by just testing your code:
Fatal error: Properties cannot be declared abstract in ... on line 3
No, there is not. Properties cannot be declared abstract in PHP.
However you can implement a getter/setter function abstract, this might be what you're looking for.
Properties aren't implemented (especially public properties), they just exist (or not):
$foo = new Foo;
$foo->publicProperty = 'Bar';
PHP 7 makes it quite a bit easier for making abstract "properties". Just as above, you will make them by creating abstract functions, but with PHP 7 you can define the return type for that function, which makes things a lot easier when you're building a base class that anyone can extend.
<?php
abstract class FooBase {
abstract public function FooProp(): string;
abstract public function BarProp(): BarClass;
public function foo() {
return $this->FooProp();
}
public function bar() {
return $this->BarProp()->name();
}
}
class BarClass {
public function name() {
return 'Bar!';
}
}
class FooClass extends FooBase {
public function FooProp(): string {
return 'Foo!';
}
public function BarProp(): BarClass {
// This would not work:
// return 'not working';
// But this will!
return new BarClass();
}
}
$test = new FooClass();
echo $test->foo() . PHP_EOL;
echo $test->bar() . PHP_EOL;
if tablename value will never change during the object's lifetime, following will be a simple yet safe implementation.
abstract class Foo_Abstract {
abstract protected function getTablename();
public function showTableName()
{
echo 'my table name is '.$this->getTablename();
}
}
class Foo extends Foo_Abstract {
//Foo must 'implement' getTablename()
protected function getTablename()
{
return 'users';
}
}
the key here is that the string value 'users' is specified and returned directly in getTablename() in child class implementation. The function mimics a "readonly" property.
This is fairly similar to a solution posted earlier on which uses an additional variable. I also like Marco's solution though it can be a bit more complicated.
Just define the property in the base class without assigning it a (default) value.
Getting the property value without redefining it with a default value or assigning it a value will throw an Error.
<?php
class Base {
protected string $name;
public function i_am() : string {
return $this->name;
}
}
class Wrong extends Base {
...
}
class Good extends Base {
protected string $name = 'Somebody';
}
$test = new Good();
echo $test->i_am(), '<br>'; // Will show "Nobody"
$test = new Wrong();
echo $test->i_am(), '<br>'; // Will throw an Error:
// Error: Typed property Base::$name must not be accessed before initialization in ....
?>
You can define a static property in an abstract class.
<?php
abstract class Foo {
private static $bar = "1234";
public static function func() {
echo self::$bar;
}
}
Foo::func(); // It will be printed 1234
Too late to answer the question, but you may use the difference between self and static as follows
<?php
class A { // Base Class
protected static $name = 'ClassA';
public static function getSelfName() {
return self::$name;
}
public static function getStaticName() {
return static::$name;
}
}
class B extends A {
protected static $name = 'ClassB';
}
echo A::getSelfName(); // ClassA
echo A::getStaticName(); // ClassA
echo B::getSelfName(); // ClassA
echo B::getStaticName(); // ClassB
is it possible to easily and quickly "assigning properties of one object to another"
class a {
public $number_one;
public $number_two;
public $number_three;
function __contruct() {
//do stuff
}
}
class b {
public $my_var;
function __contruct() {
$instanc_a = new a();
extract( $instance ); // but make these extracted object properties of class b????
// how? :-(
echo $this->number_one;
}
}
You can use get_object_vars to copy the public (only) properties of class a to the current object:
class b {
public $my_var;
function __construct() {
$instanc_a = new a();
$vars = get_object_vars($instanc_a);
foreach($vars as $name => $value) {
$this->$name = $value;
}
echo $this->number_one;
}
}
See it in action.
Note: You have a typo in your code (two cases of "contruct" instead of "construct") which will prevent things from working as they should.
Sounds like you actually want class b to extend class a
class b extends a {
public $my_var;
function __construct () {
parent::__construct();
// Now $this refers to anything in class b, or if it doesn't exist here, looks to class a for it
echo $this->number_one;
}
}
I have a class which initiates another class, i'm not concerned with having a reference to the object i only need the method and have to pass in new parameters.
class A {
__set .....
}
class B extends A {
$anotherA = new A;
$anotherA->myName = 'stackoverflow';
}
in short i'd like to have class B extend A, init a new instance of A but i don't want to have to type "new" everytime, i've seen the following syntax:
B::A // something like that
but not sure if how to use it or if that would do what i'm trying to do?
What you could do is define a static method on the class that returns the new instance. It's basically a 'shortcut', but it does exactly the same in the background.
class C {
public static function instance()
{
return new C();
}
public function instanceMethod()
{
echo 'Hello World!';
}
}
Now you can call it like:
C::instance()->instanceMethod();
Here are some examples of static functions - they can be called without using 'new A' or 'new B'.
class A {
static function message($msg = 'I am Alpha') {
echo "hi there, $msg\n";
}
}
class B {
static function message() {
A::message("I am Beta");
}
}
A::message();
B::message();
I would create the instance of A in B's constructor, then you can instantiate B using either its constructor or static B::create(), which just acts as a shortcut. You could make the constructor private if you wanted all instantiation go through create().
class A {
// __set .....
}
class B extends A {
public function __construct() {
parent::__construct();
$anotherA = new A;
$anotherA->myName = 'stackoverflow';
}
public static function create() {
return new self();
}
}
new B();
B::create();
Since you are extending A in B, you could call the method of class A:
class B extends A {
public function someMethod() {
parent::someMethodName();
}
}
Alternatively, you could create a static method in the class:
class A {
public static function someStaticMethod() { ... }
}
A::someStaticMethod();
If you really want a new instance of A, you have to use the new operator. That's what it is for.