Hướng dẫn dùng mime define trong PHP

A constant is an identifier (name) for a simple value. As the name suggests, that value cannot change during the execution of the script (except for magic constants, which aren't actually constants). Constants are case-sensitive. By convention, constant identifiers are always uppercase.

Note:

Prior to PHP 8.0.0, constants defined using the define() function may be case-insensitive.

The name of a constant follows the same rules as any label in PHP. A valid constant name starts with a letter or underscore, followed by any number of letters, numbers, or underscores. As a regular expression, it would be expressed thusly: ^[a-zA-Z_\x80-\xff][a-zA-Z0-9_\x80-\xff]*$

It is possible to define() constants with reserved or even invalid names, whose value can only be retrieved with the constant() function. However, doing so is not recommended.

Example #1 Valid and invalid constant names

// Valid constant names
define("FOO", "something");
define("FOO2", "something else");
define("FOO_BAR", "something more");

// Invalid constant names
define("2FOO", "something");

// This is valid, but should be avoided:
// PHP may one day provide a magical constant
// that will break your script
define("__FOO__", "something");

?>

Note: For our purposes here, a letter is a-z, A-Z, and the ASCII characters from 128 through 255 (0x80-0xff).

Like superglobals, the scope of a constant is global. Constants can be accessed from anywhere in a script without regard to scope. For more information on scope, read the manual section on variable scope.

Note: As of PHP 7.1.0, class constant may declare a visibility of protected or private, making them only available in the hierarchical scope of the class in which it is defined.

Function names follow the same rules as other labels in PHP. A valid function 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]*$.

Functions need not be defined before they are referenced, except when a function is conditionally defined as shown in the two examples below.

When a function is defined in a conditional manner such as the two examples shown. Its definition must be processed prior to being called.

Example #2 Conditional functions

$makefoo = true;

/* We can't call foo() from here
since it doesn't exist yet,
but we can call bar() */

bar();

if ($makefoo) {
function foo()
{
echo "I don't exist until program execution reaches me.\n";
}
}

/* Now we can safely call foo()
since $makefoo evaluated to true */

if ($makefoo) foo();

function bar()
{
echo "I exist immediately upon program start.\n";
}

?>

Example #3 Functions within functions

^[a-zA-Z_\x80-\xff][a-zA-Z0-9_\x80-\xff]*$0

^[a-zA-Z_\x80-\xff][a-zA-Z0-9_\x80-\xff]*$1

^[a-zA-Z_\x80-\xff][a-zA-Z0-9_\x80-\xff]*$2

^[a-zA-Z_\x80-\xff][a-zA-Z0-9_\x80-\xff]*$3

bar();

?>

All functions and classes in PHP have the global scope - they can be called outside a function even if they were defined inside and vice versa.

PHP does not support function overloading, nor is it possible to undefine or redefine previously-declared functions.

Note: Function names are case-insensitive for the ASCII characters ^[a-zA-Z_\x80-\xff][a-zA-Z0-9_\x80-\xff]*$6 to ^[a-zA-Z_\x80-\xff][a-zA-Z0-9_\x80-\xff]*$7, though it is usually good form to call functions as they appear in their declaration.

Both and are supported in functions. See also the function references for func_num_args(), func_get_arg(), and func_get_args() for more information.

It is possible to call recursive functions in PHP.

Example #4 Recursive functions

^[a-zA-Z_\x80-\xff][a-zA-Z0-9_\x80-\xff]*$8

Note: Recursive function/method calls with over 100-200 recursion levels can smash the stack and cause a termination of the current script. Especially, infinite recursion is considered a programming error.

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.

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:

$this is defined (A)

Fatal error: Uncaught Error: Non-static method A::foo() cannot be called statically in %s :27
Stack trace:
#0 {main}
  thrown in %s  on line 27

0.

A class may contain its own constants, variables (called "properties"), and functions (called "methods").

Example #1 Simple Class definition

$this is defined (A)

Fatal error: Uncaught Error: Non-static method A::foo() cannot be called statically in %s :27
Stack trace:
#0 {main}
  thrown in %s  on line 27

1

$this is defined (A)

Fatal error: Uncaught Error: Non-static method A::foo() cannot be called statically in %s :27
Stack trace:
#0 {main}
  thrown in %s  on line 27

2

The pseudo-variable $this is available when a method is called from within an object context. $this is the value of the calling object.

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

$this is defined (A)

Fatal error: Uncaught Error: Non-static method A::foo() cannot be called statically in %s :27
Stack trace:
#0 {main}
  thrown in %s  on line 27

3

$this is defined (A)

Fatal error: Uncaught Error: Non-static method A::foo() cannot be called statically in %s :27
Stack trace:
#0 {main}
  thrown in %s  on line 27

4

$this is defined (A)

Fatal error: Uncaught Error: Non-static method A::foo() cannot be called statically in %s :27
Stack trace:
#0 {main}
  thrown in %s  on line 27

5

$this is defined (A)

Fatal error: Uncaught Error: Non-static method A::foo() cannot be called statically in %s :27
Stack trace:
#0 {main}
  thrown in %s  on line 27

6

$this is defined (A)

Fatal error: Uncaught Error: Non-static method A::foo() cannot be called statically in %s :27
Stack trace:
#0 {main}
  thrown in %s  on line 27

7

$this is defined (A)

Fatal error: Uncaught Error: Non-static method A::foo() cannot be called statically in %s :27
Stack trace:
#0 {main}
  thrown in %s  on line 27

8

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 32

Deprecated: 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 :27
Stack trace:
#0 {main}
  thrown in %s  on line 27

Readonly classes

As of PHP 8.2.0, a class can be marked with the readonly modifier. Marking a class as readonly will add the to every declared property, and prevent the creation of . Moreover, it is impossible to add support for them by using the AllowDynamicProperties attribute. Attempting to do so will trigger a compile-time error.

$this is defined (A)

Fatal error: Uncaught Error: Non-static method A::foo() cannot be called statically in %s :27
Stack trace:
#0 {main}
  thrown in %s  on line 27

9

object(ClassA)#1 (0) {
}
object(ClassB)#1 (0) {
}
object(ClassC)#1 (0) {
}
object(ClassD)#1 (0) {
}

0

As neither untyped, nor static properties can be marked with the

object(ClassA)#1 (0) {
}
object(ClassB)#1 (0) {
}
object(ClassC)#1 (0) {
}
object(ClassD)#1 (0) {
}

1 modifier, readonly classes cannot declare them either:

object(ClassA)#1 (0) {
}
object(ClassB)#1 (0) {
}
object(ClassC)#1 (0) {
}
object(ClassD)#1 (0) {
}

2

object(ClassA)#1 (0) {
}
object(ClassB)#1 (0) {
}
object(ClassC)#1 (0) {
}
object(ClassD)#1 (0) {
}

3

object(ClassA)#1 (0) {
}
object(ClassB)#1 (0) {
}
object(ClassC)#1 (0) {
}
object(ClassD)#1 (0) {
}

4

object(ClassA)#1 (0) {
}
object(ClassB)#1 (0) {
}
object(ClassC)#1 (0) {
}
object(ClassD)#1 (0) {
}

5

A readonly class can be if, and only if, the child class is also a readonly class.

new

To create an instance of a class, the

object(ClassA)#1 (0) {
}
object(ClassB)#1 (0) {
}
object(ClassC)#1 (0) {
}
object(ClassD)#1 (0) {
}

6 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

object(ClassA)#1 (0) {
}
object(ClassB)#1 (0) {
}
object(ClassC)#1 (0) {
}
object(ClassD)#1 (0) {
}

6, 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

object(ClassA)#1 (0) {
}
object(ClassB)#1 (0) {
}
object(ClassC)#1 (0) {
}
object(ClassD)#1 (0) {
}

8

object(ClassA)#1 (0) {
}
object(ClassB)#1 (0) {
}
object(ClassC)#1 (0) {
}
object(ClassD)#1 (0) {
}

9

As of PHP 8.0.0, using

object(ClassA)#1 (0) {
}
object(ClassB)#1 (0) {
}
object(ClassC)#1 (0) {
}
object(ClassD)#1 (0) {
}

6 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

NULL
NULL
object(SimpleClass)#1 (1) {
   ["var"]=>
     string(30) "$assigned will have this value"
}

1 constant.

NULL
NULL
object(SimpleClass)#1 (1) {
   ["var"]=>
     string(30) "$assigned will have this value"
}

2

NULL
NULL
object(SimpleClass)#1 (1) {
   ["var"]=>
     string(30) "$assigned will have this value"
}

3

NULL
NULL
object(SimpleClass)#1 (1) {
   ["var"]=>
     string(30) "$assigned will have this value"
}

4

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

NULL
NULL
object(SimpleClass)#1 (1) {
   ["var"]=>
     string(30) "$assigned will have this value"
}

5 and

NULL
NULL
object(SimpleClass)#1 (1) {
   ["var"]=>
     string(30) "$assigned will have this value"
}

6.

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

object(ClassA)#1 (0) {
}
object(ClassB)#1 (0) {
}
object(ClassC)#1 (0) {
}
object(ClassD)#1 (0) {
}

8

NULL
NULL
object(SimpleClass)#1 (1) {
   ["var"]=>
     string(30) "$assigned will have this value"
}

8

NULL
NULL
object(SimpleClass)#1 (1) {
   ["var"]=>
     string(30) "$assigned will have this value"
}

9

bool(true)
bool(true)
bool(true)

0

bool(true)
bool(true)
bool(true)

1

The above example will output:

NULL
NULL
object(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

bool(true)
bool(true)
bool(true)

2

bool(true)
bool(true)
bool(true)

3

bool(true)
bool(true)
bool(true)

4

bool(true)
bool(true)
bool(true)

5

bool(true)
bool(true)
bool(true)

6

The above example will output:

bool(true)
bool(true)
bool(true)

It is possible to access a member of a newly created object in a single expression:

Example #7 Access member of newly created object

bool(true)
bool(true)
bool(true)

7

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

bool(true)
bool(true)
bool(true)

8

bool(true)
bool(true)
bool(true)

9

Extending class
a default value

0

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

Extending class
a default value

1

Extending class
a default value

2

Extending class
a default value

3

Extending class
a default value

4

The above example will output:

extends

A class can inherit the constants, methods, and properties of another class by using the keyword

Extending class
a default value

5 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

Extending class
a default value

6

Extending class
a default value

7

The above example will output:

Extending class
a default value

Signature compatibility rules

When 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

Extending class
a default value

8 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 , and

Extending class
a default value

9 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

Fatal error: Declaration of Extend::foo() must be compatible with Base::foo(int $a = 5) in /in/evtlq on line 13

0

Fatal error: Declaration of Extend::foo() must be compatible with Base::foo(int $a = 5) in /in/evtlq on line 13

1

Fatal error: Declaration of Extend::foo() must be compatible with Base::foo(int $a = 5) in /in/evtlq on line 13

2

Fatal error: Declaration of Extend::foo() must be compatible with Base::foo(int $a = 5) in /in/evtlq on line 13

3

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

Fatal error: Declaration of Extend::foo() must be compatible with Base::foo(int $a = 5) in /in/evtlq on line 13

4

Fatal error: Declaration of Extend::foo() must be compatible with Base::foo(int $a = 5) in /in/evtlq on line 13

5

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 13

Example #13 Fatal error when a child method makes an optional parameter mandatory

Fatal error: Declaration of Extend::foo() must be compatible with Base::foo(int $a = 5) in /in/evtlq on line 13

4

Fatal error: Declaration of Extend::foo() must be compatible with Base::foo(int $a = 5) in /in/evtlq on line 13

7

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 13

Warning

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 are used.

Example #14 Error when using named arguments and parameters were renamed in a child class

Fatal error: Declaration of Extend::foo() must be compatible with Base::foo(int $a = 5) in /in/evtlq on line 13

8

Fatal error: Declaration of Extend::foo() must be compatible with Base::foo(int $a = 5) in /in/evtlq on line 13

9

Fatal error: Declaration of Extend::foo(int $a) must be compatible with Base::foo(int $a = 5) in /in/qJXVC on line 13

0

Fatal error: Declaration of Extend::foo(int $a) must be compatible with Base::foo(int $a = 5) in /in/qJXVC on line 13

1

The above example will output something similar to:

Fatal error: Uncaught Error: Unknown named parameter $foo in /in/XaaeN:14
Stack 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

Fatal error: Declaration of Extend::foo(int $a) must be compatible with Base::foo(int $a = 5) in /in/qJXVC on line 13

3 use

Fatal error: Declaration of Extend::foo(int $a) must be compatible with Base::foo(int $a = 5) in /in/qJXVC on line 13

4. This is particularly useful with namespaced classes.

Example #15 Class name resolution

Fatal error: Declaration of Extend::foo(int $a) must be compatible with Base::foo(int $a = 5) in /in/qJXVC on line 13

5

Fatal error: Declaration of Extend::foo(int $a) must be compatible with Base::foo(int $a = 5) in /in/qJXVC on line 13

6

The above example will output:

Note:

The class name resolution using

NULL
NULL
object(SimpleClass)#1 (1) {
   ["var"]=>
     string(30) "$assigned will have this value"
}

1 is a compile time transformation. That means at 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

Fatal error: Declaration of Extend::foo(int $a) must be compatible with Base::foo(int $a = 5) in /in/qJXVC on line 13

8

The above example will output:

As of PHP 8.0.0, the

NULL
NULL
object(SimpleClass)#1 (1) {
   ["var"]=>
     string(30) "$assigned will have this value"
}

1 constant may also be used on objects. This resolution happens at runtime, not compile time. Its effect is the same as calling get_class() on the object.

Example #17 Object name resolution

Fatal error: Uncaught Error: Unknown named parameter $foo in /in/XaaeN:14
Stack trace:
#0 {main}
  thrown in /in/XaaeN on line 14

0

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:

Fatal error: Uncaught Error: Unknown named parameter $foo in /in/XaaeN:14
Stack trace:
#0 {main}
  thrown in /in/XaaeN on line 14

1. The nullsafe operator works the same as property or method access as above, except that if the object being dereferenced is

Fatal error: Uncaught Error: Unknown named parameter $foo in /in/XaaeN:14
Stack trace:
#0 {main}
  thrown in /in/XaaeN on line 14

2 then

Fatal error: Uncaught Error: Unknown named parameter $foo in /in/XaaeN:14
Stack trace:
#0 {main}
  thrown in /in/XaaeN on line 14

2 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

Fatal error: Uncaught Error: Unknown named parameter $foo in /in/XaaeN:14
Stack trace:
#0 {main}
  thrown in /in/XaaeN on line 14

4

Fatal error: Uncaught Error: Unknown named parameter $foo in /in/XaaeN:14
Stack trace:
#0 {main}
  thrown in /in/XaaeN on line 14

5

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.