Hướng dẫn dùng dn-attributes-failure trong PHP
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Basic class definitions begin with the keyword 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
2The 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
8Output 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 classesAs 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
9object(ClassA)#1 (0) {
}
object(ClassB)#1 (0) {
}
object(ClassC)#1 (0) {
}
object(ClassD)#1 (0) {
}
0As 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) {
}
2object(ClassA)#1 (0) {
}
object(ClassB)#1 (0) {
}
object(ClassC)#1 (0) {
}
object(ClassD)#1 (0) {
}
3object(ClassA)#1 (0) {
}
object(ClassB)#1 (0) {
}
object(ClassC)#1 (0) {
}
object(ClassD)#1 (0) {
}
4object(ClassA)#1 (0) {
}
object(ClassB)#1 (0) {
}
object(ClassC)#1 (0) {
}
object(ClassD)#1 (0) {
}
5A readonly class can be if, and only if, the child class is also a readonly class. newTo 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.
Example #3 Creating an instance object(ClassA)#1 (0) {
}
object(ClassB)#1 (0) {
}
object(ClassC)#1 (0) {
}
object(ClassD)#1 (0) {
}
8object(ClassA)#1 (0) {
}
object(ClassB)#1 (0) {
}
object(ClassC)#1 (0) {
}
object(ClassD)#1 (0) {
}
9As 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) "$assigned will have this value"
}
2NULL
NULL
object(SimpleClass)#1 (1) {
["var"]=>
string(30) "$assigned will have this value"
}
3NULL
NULL
object(SimpleClass)#1 (1) {
["var"]=>
string(30) "$assigned will have this value"
}
4Output of the above example in PHP 8: object(ClassA)#1 (0) {
}
object(ClassB)#1 (0) {
}
object(ClassC)#1 (0) {
}
object(ClassD)#1 (0) {
}
In the class context, it is possible to create a new object by NULL
NULL
object(SimpleClass)#1 (1) {
["var"]=>
string(30) "$assigned will have this value"
}
5 and NULL
NULL
object(SimpleClass)#1 (1) {
["var"]=>
string(30) "$assigned will have this value"
}
6.When assigning an already created instance of a class to a new variable, the new variable will access the same instance as the object that was assigned. This behaviour is the same when passing instances to a function. A copy of an already created object can be made by cloning it. Example #5 Object Assignment object(ClassA)#1 (0) {
}
object(ClassB)#1 (0) {
}
object(ClassC)#1 (0) {
}
object(ClassD)#1 (0) {
}
8NULL
NULL
object(SimpleClass)#1 (1) {
["var"]=>
string(30) "$assigned will have this value"
}
8NULL
NULL
object(SimpleClass)#1 (1) {
["var"]=>
string(30) "$assigned will have this value"
}
9bool(true) bool(true) bool(true)0 bool(true) bool(true) bool(true)1 The above example will output: NULL
NULL
object(SimpleClass)#1 (1) {
["var"]=>
string(30) "$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:
Properties and methodsClass 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 value0 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 value1 Extending class a default value2 Extending class a default value3 Extending class a default value4 The above example will output: extendsA class can inherit the constants, methods, and properties of another class by using the keyword Extending class a default value5 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::.
Example #10 Simple Class Inheritance Extending class a default value6 Extending class a default value7 The above example will output: Extending class a 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 Extending class a default value8 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 value9 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 130 Fatal error: Declaration of Extend::foo() must be compatible with Base::foo(int $a = 5) in /in/evtlq on line 131 Fatal error: Declaration of Extend::foo() must be compatible with Base::foo(int $a = 5) in /in/evtlq on line 132 Fatal error: Declaration of Extend::foo() must be compatible with Base::foo(int $a = 5) in /in/evtlq on line 133 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 134 Fatal error: Declaration of Extend::foo() must be compatible with Base::foo(int $a = 5) in /in/evtlq on line 135 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 134 Fatal error: Declaration of Extend::foo() must be compatible with Base::foo(int $a = 5) in /in/evtlq on line 137 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 138 Fatal error: Declaration of Extend::foo() must be compatible with Base::foo(int $a = 5) in /in/evtlq on line 139 Fatal error: Declaration of Extend::foo(int $a) must be compatible with Base::foo(int $a = 5) in /in/qJXVC on line 130 Fatal error: Declaration of Extend::foo(int $a) must be compatible with Base::foo(int $a = 5) in /in/qJXVC on line 131 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
::classThe Fatal error: Declaration of Extend::foo(int $a) must be compatible with Base::foo(int $a = 5) in /in/qJXVC on line 133 use Fatal error: Declaration of Extend::foo(int $a) must be compatible with Base::foo(int $a = 5) in /in/qJXVC on line 134. 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 135 Fatal error: Declaration of Extend::foo(int $a) must be compatible with Base::foo(int $a = 5) in /in/qJXVC on line 136 The above example will output:
As of PHP 8.0.0, the NULL
NULL
object(SimpleClass)#1 (1) {
["var"]=>
string(30) "$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
0The above example will output: Nullsafe methods and propertiesAs 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
4Fatal error: Uncaught Error: Unknown named parameter $foo in /in/XaaeN:14
Stack trace:
#0 {main}
thrown in /in/XaaeN on line 14
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