Lets say I have a class that is responsible for composing another class:
class ClassBuilder
{
protected $baseClass;
public function __construct()
{
$this->baseClass = new BaseClass();
}
public function set()
{
$this->baseClass->foo = 'bar';
}
// other methods to further modify BaseClass
}
class BaseClass
{
public $foo;
}
class ChildClass extends BaseClass {}
I want to create a method in the ClassBuilder that would allow me to update its baseClass property to an instance of ChildClass with the same property values as the current BaseClass object. How can I do that?
public function update()
{
// $this->baseClass = new ChildClass() with the current property values in BaseClass
}
I'm not sure that your overall approach is correct, but about the only way is to loop and set:
public function update()
{
$new = new ChildClass();
foreach($this->baseClass as $name => $value) {
$new->$name = $value;
}
$this->baseClass = $new;
//or
$this->baseClass = clone $new;
}
my question is very easy.I have a trait and child class.
trait mixVar {
public function go(){
return [];
}
}
class example extends foo {
use mixVar;
public $var=$this->go(); //does not work
}
how to make this in php?
You cannot use a method call to assign a default value to a property. You would have to do it in the constructor.
class example extends foo
{
use mixVar;
public $var;
public function __construct()
{
$this->var = $this->go();
}
}
Another solution is to define trait method like:
trait mixVar {
public function go(){
$this->var = []; // your value here
}
}
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 been see this come up alot i think it has todo with late static binding but whats the point of doing it this way.
class {
public static $name = array();
function something() {
static::$name;
}
}
over
class {
public static $name = array();
function something() {
self::$name;
}
}
self::$name in the parent class will always refer to the parent class' property whereas static::$name in the parent class will refer to the property of the runtime class.
For example
class A
{
protected static $foo = 'foo';
public static function getSelfFoo()
{
return self::$foo;
}
public static function getStaticFoo()
{
return static::$foo;
}
}
class B extends A
{
protected static $foo = 'bar';
}
echo A::getSelfFoo(); // 'foo'
echo A::getStaticFoo(); // 'foo'
echo B::getSelfFoo(); // 'foo'
echo B::getStaticFoo(); // 'bar'
It matters if you create a subclass of your class. In your first example, the something function will refer to the $name variable on the subclass. In your second example it will refer to the $name variable on the base class.