Mẹo Hướng dẫn Hướng dẫn dùng method synonym trong PHP 2022
Cao Thị Xuân Dung đang tìm kiếm từ khóa Hướng dẫn dùng method synonym trong PHP được Cập Nhật vào lúc : 2022-09-25 18:48:09 . Với phương châm chia sẻ Bí quyết về trong nội dung bài viết một cách Chi Tiết 2022. Nếu sau khi đọc tài liệu vẫn ko hiểu thì hoàn toàn có thể lại Comments ở cuối bài để Admin lý giải và hướng dẫn lại nha.class
Basic class definitions begin with the keyword class, followed by a class name, followed by a pair of curly braces which enclose the definitions of the properties and methods belonging to the class.
Nội dung chính- Properties and methods Nullsafe methods and properties
The class name can be any valid label, provided it is not a PHP reserved word. A valid class name starts with a letter or underscore, followed by any number of letters, numbers, or underscores. As a regular expression, it would be expressed thus: ^[a-zA-Z_x80-xff][a-zA-Z0-9_x80-xff]*$.
A class may contain its own constants, variables (called “properties”), and functions (called “methods”).
Hướng dẫn dùng object synonym trong PHP
Example #1 Simple Class definition
class SimpleClass
// property declaration
public $var = 'a default value';// method declaration
public function displayVar()
echo $this->var;
?>
The pseudo-variable $this is available when a method is called from within an object context. $this is the value of the calling object.
Hướng dẫn dùng object synonym trong PHP
Warning
Calling a non-static method statically throws an Error. Prior to PHP 8.0.0, this would generate a deprecation notice, and $this would be undefined.
Example #2 Some examples of the $this pseudo-variable
Hướng dẫn dùng object synonym trong PHP
class A
function foo()
if (isset($this))
echo '$this is defined (';
echo get_class($this);
echo ")n";
else
echo "$this is not defined.n";
class
B
function bar()
A::foo();
$a = new A();
$a->foo();A::foo();$b = new B();
$b->bar();B::bar();
?>
Output of the above example in PHP 7:
$this is defined (A)Deprecated: Non-static method A::foo() should not be called statically in %s on line 27$this is not defined.Deprecated: Non-static method A::foo() should not be called statically in %s on line 20$this is not defined.Deprecated: Non-static method B::bar() should not be called statically in %s on line 32Deprecated: Non-static method A::foo() should not be called statically in %s on line 20$this is not defined.Output of the above example in PHP 8:
$this is defined (A)Fatal error: Uncaught Error: Non-static method A::foo() cannot be called statically in %s :27Stack trace:#0 main thrown in %s on line 27new
To create an instance of a class, the new keyword must be used. An object will always be created unless the object has a constructor defined that throws an exception on error. Classes should be defined before instantiation (and in some cases this is a requirement).
If a string containing the name of a class is used with new, a new instance of that class will be created. If the class is in a namespace, its fully qualified name must be used when doing this.
Note:
If there are no arguments to be passed to the class’s constructor, parentheses after the class name may be omitted.
Example #3 Creating an instance
$instance = new SimpleClass();// This can also be done with a variable:
$className = 'SimpleClass';
$instance = new $className(); // new SimpleClass()
?>
As of PHP 8.0.0, using new with arbitrary expressions is supported. This allows more complex instantiation if the expression produces a string. The expressions must be wrapped in parentheses.
Example #4 Creating an instance using an arbitrary expression
In the given example we show multiple examples of valid arbitrary expressions that produce a class name. This shows a call to a function, string concatenation, and the ::class constant.
class ClassB extends stdClass
class ClassC extends ClassB
class ClassD extends ClassA
function
getSomeClass(): string
return 'ClassA';
var_dump(new (getSomeClass()));
var_dump(new ('Class' . 'B'));
var_dump(new ('Class' . 'C'));
var_dump(new (ClassD::class));
?>
Output of the above example in PHP 8:
object(ClassA)#1 (0) object(ClassB)#1 (0) object(ClassC)#1 (0) object(ClassD)#1 (0)In the class context, it is possible to create a new object by new self and new parent.
When assigning an already created instance of a class to a new variable, the new variable will access the same instance as the object that was assigned. This behaviour is the same when passing instances to a function. A copy of an already created object can be made by cloning it.
Example #5 Object Assignment
$instance
= new SimpleClass();$assigned = $instance;
$reference =& $instance;$instance->var = '$assigned will have this value';$instance = null; // $instance and $reference become nullvar_dump($instance);
var_dump($reference);
var_dump($assigned);
?>
The above example will output:
NULLNULLobject(SimpleClass)#1 (1) ["var"]=> string(30) "$assigned will have this value"It’s possible to create instances of an object in a couple of ways:
Example #6 Creating new objects
class Test
static public function getNew()
return new static;
class
Child extends Test
$obj1 = new Test();
$obj2 = new $obj1;
var_dump($obj1 !== $obj2);$obj3 = Test::getNew();
var_dump($obj3 instanceof Test);$obj4 = Child::getNew();
var_dump($obj4 instanceof Child);
?>
The above example will output:
bool(true)bool(true)bool(true)It is possible to access a thành viên of a newly created object in a single expression:
Example #7 Access thành viên of newly created object
echo (new DateTime())->format('Y');
?>
The above example will output something similar to:
Note: Prior to PHP 7.1, the arguments are not evaluated if there is no constructor function defined.
Properties and methods
Class properties and methods live in separate “namespaces”, so it is possible to have a property and a method with the same name. Referring to both a property and a method has the same notation, and whether a property will be accessed or a method will be called, solely depends on the context, i.e. whether the usage is a variable access or a function call.
Example #8 Property access vs. method call
class Foo
public $bar = 'property';
public function
bar()
return 'method';
$obj = new Foo();
echo $obj->bar, PHP_EOL, $obj->bar(), PHP_EOL;
The above example will output:
That means that calling an anonymous function which has been assigned to a property is not directly possible. Instead the property has to be assigned to a variable first, for instance. It is possible to call such a property directly by enclosing it in parentheses.
Example #9 Calling an anonymous function stored in a property
class Foo
public $bar;
public function
__construct()
$this->bar = function()
return 42;
;
$obj = new Foo();
echo (
$obj->bar)(), PHP_EOL;
The above example will output:
extends
A class can inherit the constants, methods, and properties of another class by using the keyword extends in the class declaration. It is not possible to extend multiple classes; a class can only inherit from one base class.
The inherited constants, methods, and properties can be overridden by redeclaring them with the same name defined in the parent class. However, if the parent class has defined a method or constant as final, they may not be overridden. It is possible to access the overridden methods or static properties by referencing them with parent::.
Note: As of PHP 8.1.0, constants may be declared as final.
Example #10 Simple Class Inheritance
class ExtendClass extends SimpleClass
// Redefine the parent method
function displayVar()
echo "Extending classn";
parent::displayVar();
$extended = new ExtendClass();
$extended->displayVar();
?>
The above example will output:
Extending classa default value Signature compatibility rulesWhen overriding a method, its signature must be compatible with the parent method. Otherwise, a fatal error is emitted, or, prior to PHP 8.0.0, an E_WARNING level error is generated. A signature is compatible if it respects the variance rules, makes a mandatory parameter optional, and if any new parameters are optional. This is known as the Liskov Substitution Principle, or LSP for short. The constructor, and private methods are exempt from these signature compatibility rules, and thus won’t emit a fatal error in case of a signature mismatch.
Example #11 Compatible child methods
public function foo(int $a)
echo "Validn";
class
Extend1 extends Base
function foo(int $a = 5)
parent::foo($a);
class
Extend2 extends Base
function foo(int $a, $b = 5)
parent::foo($a);
$extended1 = new Extend1();
$extended1->foo();
$extended2 = new Extend2();
$extended2->foo(1);
The above example will output:
The following examples demonstrate that a child method which removes a parameter, or makes an optional parameter mandatory, is not compatible with the parent method.
Example #12 Fatal error when a child method removes a parameter
public function foo(int $a = 5)
echo "Validn";
class
Extend extends Base
function foo()
parent::foo(1);
Output of the above example in PHP 8 is similar to:
Fatal error: Declaration of Extend::foo() must be compatible with Base::foo(int $a = 5) in /in/evtlq on line 13Example #13 Fatal error when a child method makes an optional parameter mandatory
public function foo(int $a = 5)
echo "Validn";
class
Extend extends Base
function foo(int $a)
parent::foo($a);
Output of the above example in PHP 8 is similar to:
Fatal error: Declaration of Extend::foo(int $a) must be compatible with Base::foo(int $a = 5) in /in/qJXVC on line 13Warning
Renaming a method’s parameter in a child class is not a signature incompatibility. However, this is discouraged as it will result in a runtime Error if named arguments are used.
Example #14 Error when using named arguments and parameters were renamed in a child class
public function test($foo, $bar)
class
B extends A
public function test($a, $b)
$obj = new B;// Pass parameters according to A::test() contract
$obj->test(foo: "foo", bar: "bar"); // ERROR!
The above example will output something similar to:
Fatal error: Uncaught Error: Unknown named parameter $foo in /in/XaaeN:14Stack trace:#0 main thrown in /in/XaaeN on line 14::class
The class keyword is also used for class name resolution. To obtain the fully qualified name of a class ClassName use ClassName::class. This is particularly useful with namespaced classes.
Example #15 Class name resolution
namespace NS
class ClassName
echo
ClassName::class;
?>
The above example will output:
Note:
The class name resolution using ::class is a compile time transformation. That means the time the class name string is created no autoloading has happened yet. As a consequence, class names are expanded even if the class does not exist. No error is issued in that case.
Example #16 Missing class name resolution
print DoesNotExist::class;
?>
The above example will output:
As of PHP 8.0.0, the ::class constant may also be used on objects. This resolution happens runtime, not compile time. Its effect is the same as calling get_class() on the object.
Example #17 Object name resolution
namespace NS
class ClassName
$c = new ClassName();
print $c::class;
?>
The above example will output:
Nullsafe methods and properties
As of PHP 8.0.0, properties and methods may also be accessed with the “nullsafe” operator instead: ?->. The nullsafe operator works the same as property or method access as above, except that if the object being dereferenced is null then null will be returned rather than an exception thrown. If the dereference is part of a chain, the rest of the chain is skipped.
The effect is similar to wrapping each access in an is_null() check first, but more compact.
Example #18 Nullsafe Operator
$result = $repository?->getUser(5)?->name;// Is equivalent to the following code block:
if (is_null($repository))
$result = null;
else
$user = $repository->getUser(5);
if (is_null($user))
$result = null;
else
$result = $user->name;
?>
Note:
The nullsafe operator is best used when null is considered a valid and expected possible value for a property or method return. For indicating an error, a thrown exception is preferable.
aaron thatone dot com ¶
14 years ago
I was confused first about object assignment, because it's not quite the same as normal assignment or assignment by reference. But I think I've figured out what's going on.
First, think of variables in PHP as data slots. Each one is a name that points to a data slot that can hold a value that is one of the basic data types: a number, a string, a boolean, etc. When you create a reference, you are making a second name that points the same data slot. When you assign one variable to another, you are copying the contents of one data slot to another data slot.
Now, the trick is that object instances are not like the basic data types. They cannot be held in the data slots directly. Instead, an object's "handle" goes in the data slot. This is an identifier that points one particular instance of an obect. So, the object handle, although not directly visible to the programmer, is one of the basic datatypes.
What makes this tricky is that when you take a variable which holds an object handle, and you assign it to another variable, that other variable gets a copy of the same object handle. This means that both variables can change the state of the same object instance. But they are not references, so if one of the variables is assigned a new value, it does not affect the other variable.
// Assignment of an object
Class Object
public $foo="bar";
;$objectVar = new Object();
$reference =& $objectVar;
$assignment = $objectVar//
// $objectVar --->+---------+
// |(handle1)----+
// $reference --->+---------+ |
// |
// +---------+ |
// $assignment -->|(handle1)----+
// +---------+ |
// |
// v
// Object(1):foo="bar"
//
?>
$assignment has a different data slot from $objectVar, but its data slot holds a handle to the same object. This makes it behave in some ways like a reference. If you use the variable $objectVar to change the state of the Object instance, those changes also show up under $assignment, because it is pointing that same Object instance.
$objectVar->foo = "qux";
print_r( $objectVar );
print_r( $reference );
print_r( $assignment );//
// $objectVar --->+---------+
// |(handle1)----+
// $reference --->+---------+ |
// |
// +---------+ |
// $assignment -->|(handle1)----+
// +---------+ |
// |
// v
// Object(1):foo="qux"
//
?>
But it is not exactly the same as a reference. If you null out $objectVar, you replace the handle in its data slot with NULL. This means that $reference, which points the same data slot, will also be NULL. But $assignment, which is a different data slot, will still hold its copy of the handle to the Object instance, so it will not be NULL.
$objectVar = null;
print_r($objectVar);
print_r($reference);
print_r($assignment);//
// $objectVar --->+---------+
// | NULL |
// $reference --->+---------+
//
// +---------+
// $assignment -->|(handle1)----+
// +---------+ |
// |
// v
// Object(1):foo="qux"
?>
pawel dot zimnowodzki gmail dot com ¶
3 months ago
Although there is no null-safe operator for not existed array keys I found workaround for it: ($array['not_existed_key'] ?? null)?->methodName()
kStarbe gmail point com ¶
5 years ago
You start using :: in second example although the static concept has not been explained. This is not easy to discover when you are starting from the basics.
Doug ¶
11 years ago
What is the difference between $this and self ?
Inside a class definition, $this refers to the current object, while self refers to the current class.
It is necessary to refer to a class element using self ,
and refer to an object element using $this .
Note also how an object variable must be preceded by a keyword in its definition.
The following example illustrates a few cases:
class Classy
const
STAT = 'S' ; // no dollar sign for constants (they are always static)
static $stat = 'Static' ;
public $publ = 'Public' ;
private $priv = 'Private' ;
protected $prot = 'Protected' ;
function
__construct( )
public function
showMe( )
print '
self::STAT: ' . self::STAT ; // refer to a (static) constant like this
print '
self::$stat: ' . self::$stat ; // static variable
print '
$this->stat: ' . $this->stat ; // legal, but not what you might think: empty result
print '
$this->publ: ' . $this->publ ; // refer to an object variable like this
print '
' ;
$me = new Classy( ) ;
$me->showMe( ) ;/* Produces this output:
self::STAT: S
self::$stat: Static
$this->stat:
$this->publ: Public
*/
?>
Hayley Watson ¶
4 years ago
Class names are case-insensitive:
class Foo
class foo //Fatal error.
?>
Any casing can be used to refer to the class
class bAr
$t = new Bar();
$u = new bar();
echo ($t instanceof $u) ? "true" : "false"; // "true"
echo ($t instanceof BAR) ? "true" : "false"; // "true"
echo is_a($u, 'baR') ? "true" : "false"; // "true"
?>
But the case used when the class was defined is preserved as "canonical":
echo get_class($t); // "bAr"
?>
And, as always, "case-insensitivity" only applies to ASCII.
class пасха
class Пасха // valid
$p = new ПАСХА(); // Uncaught warning.
?>
wbcarts juno dot com ¶
14 years ago
CLASSES and OBJECTS that represent the "Ideal World"
Wouldn't it be great to get the lawn mowed by saying $son->mowLawn()? Assuming the function mowLawn() is defined, and you have a son that doesn't throw errors, the lawn will be mowed.
In the following example; let objects of type Line3D measure their own length in 3-dimensional space. Why should I or PHP have to provide another method from outside this class to calculate length, when the class itself holds all the neccessary data and has the education to make the calculation for itself?
* Point3D.php
*
* Represents one locaton or position in 3-dimensional space
* using an (x, y, z) coordinate system.
*/
class Point3D
public $x;
public $y;
public $z; // the x coordinate of this Point.
/*
* use the x and y variables inherited from Point.php.
*/
public function __construct($xCoord=0, $yCoord=0, $zCoord=0)
$this->x = $xCoord;
$this->y = $yCoord;
$this->z = $zCoord;
/*
* the (String) representation of this Point as "Point3D(x, y, z)".
*/
public function __toString()
return 'Point3D(x=' . $this->x . ', y=' . $this->y . ', z=' . $this->z . ')';
/*
* Line3D.php
*
* Represents one Line in 3-dimensional space using two Point3D objects.
*/
class Line3D
$start;
$end;
public function
__construct($xCoord1=0, $yCoord1=0, $zCoord1=0, $xCoord2=1, $yCoord2=1, $zCoord2=1)
$this->start = new Point3D($xCoord1, $yCoord1, $zCoord1);
$this->end = new Point3D($xCoord2, $yCoord2, $zCoord2);
/*
* calculate the length of this Line in 3-dimensional space.
*/
public function getLength()
return sqrt(
pow($this->start->x - $this->end->x, 2) +
pow($this->start->y - $this->end->y, 2) +
pow($this->start->z - $this->end->z, 2)
);
/*
* The (String) representation of this Line as "Line3D[start, end, length]".
*/
public function __toString()
return 'Line3D[start=" . $this->start .
", end=' . $this->end .
', length=" . $this->getLength() . "]';
/*
* create and display objects of type Line3D.
*/
echo '
' . (new Line3D()) . "
n";echo '
' . (new Line3D(0, 0, 0, 100, 100, 0)) . "
n";echo '
' . (new Line3D(0, 0, 0, 100, 100, 100)) . "
n";?><-- The results look like this -->
Line3D[start=Point3D(x=0, y=0, z=0), end=Point3D(x=1, y=1, z=1), length=1.73205080757]
Line3D[start=Point3D(x=0, y=0, z=0), end=Point3D(x=100, y=100, z=0), length=141.421356237]
Line3D[start=Point3D(x=0, y=0, z=0), end=Point3D(x=100, y=100, z=100), length=173.205080757]
My absolute favorite thing about OOP is that "good" objects keep themselves in check. I mean really, it's the exact same thing in reality... like, if you hire a plumber to fix your kitchen sink, wouldn't you expect him to figure out the best plan of attack? Wouldn't he dislike the fact that you want to control the whole job? Wouldn't you expect him to not give you additional problems? And for god's sake, it is too much to ask that he cleans up before he leaves?
I say, design your classes well, so they can do their jobs uninterrupted... who like bad news? And, if your classes and objects are well defined, educated, and have all the necessary data to work on (like the examples above do), you won't have to micro-manage the whole program from outside of the class. In other words... create an object, and LET IT RIP!
Notes on stdClass ¶
13 years ago
stdClass is the default PHP object. stdClass has no properties, methods or parent. It does not support magic methods, and implements no interfaces.
When you cast a scalar or array as Object, you get an instance of stdClass. You can use stdClass whenever you need a generic object instance.
// ways of creating stdClass instances
$x = new stdClass;
$y = (object) null; // same as above
$z = (object) 'a'; // creates property 'scalar' = 'a'
$a = (object) array('property1' => 1, 'property2' => 'b');
?>
stdClass is NOT a base class! PHP classes do not automatically inherit from any class. All classes are standalone, unless they explicitly extend another class. PHP differs from many object-oriented languages in this respect.
// CTest does not derive from stdClass
class CTest
public $property1;
$t = new CTest;
var_dump($t instanceof stdClass); // false
var_dump(is_subclass_of($t, 'stdClass')); // false
echo get_class($t) . "n"; // 'CTest'
echo get_parent_class($t) . "n"; // false (no parent)
?>
You cannot define a class named 'stdClass' in your code. That name is already used by the system. You can define a class named 'Object'.
You could define a class that extends stdClass, but you would get no benefit, as stdClass does nothing.
(tested on PHP 5.2.8)
Anonymous ¶
4 years ago
At first I was also confused by the assignment vs referencing but here's how I was finally able to get my head around it. This is another example which is somewhat similar to one of the comments but can be helpful to those who did not understand the first example. Imagine object instances as rooms where you can store and manipulate your properties and functions. The variable that contains the object simply holds 'a key' to this room and thus access to the object. When you assign this variable to another new variable, what you are doing is you're making a copy of the key and giving it to this new variable. That means these two variable now have access to the same 'room' (object) and can thus get in and manipulate the values. However, when you create a reference, what you doing is you're making the variables SHARE the same key. They both have access to the room. If one of the variable is given a new key, then the key that they are sharing is replaced and they now share a new different key. This does not affect the other variable with a copy of the old key...that variable still has access to the first room
johannes dot kingma gmail dot com ¶
9 months ago
BEWARE!
Like Hayley Watson pointed out class names are not case sensitive.
class Foo
class foo // Fatal error: Cannot declare class foo, because the name is already in use
?>
As well as
class BAR
$bar = new Bar();
echo get_class($bar);
?>
Is perfectly fine and will return 'BAR'.
This has implications on autoloading classes though. The standard spl_autoload function will strtolower the class name to cope with case in-sensitiveness and thus the class BAR can only be found if the file name is bar.php (or another variety if an extension was registered with spl_autoload_extensions(); ) not BAR.php for a case sensitive file and operating system like linux. Windows file system is case sensitive but the OS is not and there for autoloading BAR.php will work.
moty66 gmail dot com ¶
13 years ago
I hope that this will help to understand how to work with static variables inside a class
public static
$foo = 'I am foo';
public $bar = 'I am bar';
public static function
getFoo() echo self::$foo;
public static function setFoo() self::$foo = 'I am a new foo';
public function getBar() echo $this->bar;
$ob = new a();
a::getFoo(); // output: I am foo
$ob->getFoo(); // output: I am foo
//a::getBar(); // fatal error: using $this not in object context
$ob->getBar(); // output: I am bar
// If you keep $bar non static this will work
// but if bar was static, then var_dump($this->bar) will output null
// unset($ob);
a::setFoo(); // The same effect as if you called $ob->setFoo(); because $foo is static
$ob = new a(); // This will have no effects on $foo
$ob->getFoo(); // output: I am a new foo ?>
Regards
Motaz Abuthiab
Jeffrey ¶
13 years ago
A PHP Class can be used for several things, but the most basic level, you'll use classes to "organize and giảm giá with like-minded data". Here's what I mean by "organizing like-minded data". First, start with unorganized data.
$customer_name;
$item_name;
$item_price;
$customer_address;
$item_qty;
$item_total;
?>
Now to organize the data into PHP classes:
class Customer
$name; // same as $customer_name
$address; // same as $customer_address
class
Item
$name; // same as $item_name
$price; // same as $item_price
$qty; // same as $item_qty
$total; // same as $item_total
?>
Now here's what I mean by "dealing" with the data. Note: The data is already organized, so that in itself makes writing new functions extremely easy.
class Customer
public $name, $address; // the data for this class...
// function to giảm giá with user-input / validation
// function to build string for output
// function to write -> database
// function to read <- database
// etc, etc
class
Item
public $name, $price, $qty, $total; // the data for this class...
// function to calculate total
// function to format numbers
// function to giảm giá with user-input / validation
// function to build string for output
// function to write -> database
// function to read <- database
// etc, etc
?>
Imagination that each function you write only calls the bits of data in that class. Some functions may access all the data, while other functions may only access one piece of data. If each function revolves around the data inside, then you have created a good class.
thisleenoble DOPEOPLESTILLNOSPAM dot me dot com ¶
1 year ago
Instantiating an object with a string variable defaults to non-namespaced scope. Given two classes in the same namespace.
namespace foo;
class
bar {
public function createSubclass(string $type)
return new $type();
?>
namespace foo;
class
baz
?>
$barObj = new bar();
$barObj->createSubclass('baz');// result: Uncaught Error: Class 'baz' not found
?>
Change bar class to:
namespace foo;
class
bar {
public function createSubclass(string $type)
type = ''.__NAMESPACE__.''.type;
return new $type();
?>
Anonymous ¶
5 years ago
Understanding what does $this exactly do:
class toop
public $i = "1234";
public function setv($a)
$this->i = $a;
public function returnthis()
return $this;
$ob = new toop();
$ob1 = new toop();
$obthis = $ob->returnthis();
echo $ob->i."n";
$ob->setv("$ob set");
echo $ob->i."n";
$obthis->setv("$obthis set");
echo $ob->i."n";
$ob1->setv('$ob1 set');
echo $ob->i."n";
?>
This will output:
1234
$ob set
$obthis set
$obthis set
