blocks|key|548757|text|没有定义属性这回事。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|548758|只能声明属性，因为它们是初始化时保留在内存中的数据的容器。|548759|另一方面，函数可以声明(类型、名称、参数)而无需定义(缺少函数体)，因此可以使其成为抽象的。|548760|"Abstract“只表示声明了但没有定义的东西，因此在使用它之前，你需要定义它，否则它就变得无用了。|548761|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|J|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|K|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|L|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|M|8|@]|9|@]|A|$]]|$1|H|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|I|$]]

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.

blocks|key|548878|text|不，没有办法强制使用编译器，您必须对$tablename变量使用运行时检查(例如，在构造函数中)，例如：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|548879|class+Foo_Abstract+{
++public+final+function+__construct(/*whatever*/)+{
++++if(!isset($this->tablename))
++++++throw+new+LogicException(get_class($this)+.+'+must+have+a+$tablename');
++}
}|code-block|syntax|javascript|548880|要对抽象的所有派生类执行此操作，您必须将Foo_+Foo_Abstract的构造函数设为final，以防止重写。|548881|你可以声明一个抽象的getter：|548882|abstract+class+Foo_Abstract+{
++abstract+public+function+get_tablename();
}

class+Foo+extends+Foo_Abstract+{
++protected+$tablename+=+'tablename';
++public+function+get_tablename()+{
++++return+$this->tablename;
++}
}|548883|entityMap^0|I|A|0|0|18|5|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|V|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|W|8|@$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|M|3|N|5|6|7|Z|8|@]|D|@]|E|$]]|$1|O|3|P|5|H|7|10|8|@]|D|@]|E|$I|J]]|$1|Q|3|-4|5|6|7|11|8|@]|D|@]|E|$]]]|R|$]]

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 <code>$tablename</code> variable, e.g.:

<pre><code>class Foo_Abstract {
 public final function __construct(/*whatever*/) {
 if(!isset($this-&gt;tablename))
 throw new LogicException(get_class($this) . ' must have a $tablename');
 }
}
</code></pre>

To enforce this for all derived classes of Foo_Abstract you would have to make Foo_Abstract's constructor <code>final</code>, preventing overriding.

You could declare an abstract getter instead:

<pre><code>abstract class Foo_Abstract {
 abstract public function get_tablename();
}

class Foo extends Foo_Abstract {
 protected $tablename = 'tablename';
 public function get_tablename() {
 return $this-&gt;tablename;
 }
}
</code></pre>

blocks|key|765674|text|如上所述，没有这样的确切定义。然而，我使用这个简单的变通方法来强制子类定义“抽象”属性：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|765675|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();
++}
}|code-block|syntax|javascript|765676|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

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:

<pre><code>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-&gt;setName();
 }
}

class Son extends Father
{
 protected function setName()
 {
 $this-&gt;name = "son";
 }

 function __construct(){
 parent::__construct();
 }
}
</code></pre>

blocks|key|548996|text|根据属性的上下文，如果我想在扩展类中强制声明抽象类属性，我喜欢在抽象对象构造函数或setter/getter方法中使用带有static关键字的常量作为属性。您可以选择使用final来防止该方法在扩展类中被重写。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|548997|示例：https://3v4l.org/WH5Xl|548998|abstract+class+AbstractFoo
{
++++public+$bar;

++++final+public+function+__construct()
++++{
++++++++$this->bar+=+static::BAR;
++++}
}

class+Foo+extends+AbstractFoo
{
++++//const+BAR+=+'foobar';+//uncomment+to+prevent+exception
}|code-block|syntax|javascript|548999|$foo+=+new+Foo();+
//Fatal+Error:+Undefined+class+constant+'BAR'|549000|549001|但是，如果重新定义，扩展类将覆盖父类属性和方法。|549002|例如，如果某个属性在父类中声明为protected，并在扩展类中重新定义为public，则生成的属性为public。否则，如果该属性在父类中声明为private，则它将保持为private，并且不可用于扩展类。|549003|http://www.php.net//manual/en/language.oop5.static.php|549004|entityMap|0|LINK|mutability|MUTABLE|url|https://www.php.net/manual/en/language.oop5.final.php|1|https://3v4l.org/WH5Xl|2^0|1P|6|2D|5|2D|5|0|0|3|M|1|0|0|0|0|0|G|9|11|6|1F|6|21|7|2F|7|0|0|1I|2|0^^$0|@$1|2|3|4|5|6|7|16|8|@$9|17|A|18|B|C]|$9|19|A|1A|B|C]]|D|@$9|1B|A|1C|1|1D]]|E|$]]|$1|F|3|G|5|6|7|1E|8|@]|D|@$9|1F|A|1G|1|1H]]|E|$]]|$1|H|3|I|5|J|7|1I|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|J|7|1J|8|@]|D|@]|E|$K|L]]|$1|O|3|-4|5|6|7|1K|8|@]|D|@]|E|$]]|$1|P|3|Q|5|6|7|1L|8|@]|D|@]|E|$]]|$1|R|3|S|5|6|7|1M|8|@$9|1N|A|1O|B|C]|$9|1P|A|1Q|B|C]|$9|1R|A|1S|B|C]|$9|1T|A|1U|B|C]|$9|1V|A|1W|B|C]]|D|@]|E|$]]|$1|T|3|U|5|6|7|1X|8|@]|D|@$9|1Y|A|1Z|1|20]]|E|$]]|$1|V|3|-4|5|6|7|21|8|@]|D|@]|E|$]]]|W|$X|$5|Y|Z|10|E|$11|12]]|13|$5|Y|Z|10|E|$11|14]]|15|$5|Y|Z|10|E|$11|U]]]]

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 <code>static</code> keyword for the property in the abstract object constructor or setter/getter methods. You can optionally use <a href="https://www.php.net/manual/en/language.oop5.final.php" rel="noreferrer"><code>final</code></a> to prevent the method from being overridden in extended classes.
Example: <a href="https://3v4l.org/WH5Xl" rel="noreferrer">https://3v4l.org/WH5Xl</a>
<pre class="lang-php prettyprint-override"><code>abstract class AbstractFoo
{
 public $bar;

 final public function __construct()
 {
 $this-&gt;bar = static::BAR;
 }
}

class Foo extends AbstractFoo
{
 //const BAR = 'foobar'; //uncomment to prevent exception
}
</code></pre>
<pre class="lang-php prettyprint-override"><code>$foo = new Foo(); 
//Fatal Error: Undefined class constant 'BAR'
</code></pre>
<hr />
However, the extended class overrides the parent class properties and methods if redefined. 
For example; if a property is declared as <code>protected</code> in the parent and redefined as <code>public</code> in the extended class, the resulting property is <code>public</code>. Otherwise, if the property is declared <code>private</code> in the parent it will remain <code>private</code> and not available to the extended class.
<a href="http://www.php.net//manual/en/language.oop5.static.php" rel="noreferrer">http://www.php.net//manual/en/language.oop5.static.php</a>

blocks|key|549067|text|如果tablename值在对象的生命周期内永远不会改变，下面是一个简单但安全的实现。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|549068|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';
++++}
}|code-block|syntax|javascript|549069|这里的关键是字符串值'users‘是在子类实现的getTablename()中直接指定和返回的。该函数模拟"readonly“属性。|549070|这与之前发布的使用额外变量的解决方案非常相似。我也喜欢Marco的解决方案，尽管它可能会更复杂一些。|549071|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

if tablename value will never change during the object's lifetime, following will be a simple yet safe implementation.

<pre><code>abstract class Foo_Abstract {
 abstract protected function getTablename();

 public function showTableName()
 {
 echo 'my table name is '.$this-&gt;getTablename();
 }
}

class Foo extends Foo_Abstract {
 //Foo must 'implement' getTablename()
 protected function getTablename()
 {
 return 'users';
 }
}
</code></pre>

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.

blocks|key|765864|text|PHP7使得创建抽象的“属性”变得相当容易。如上所述，您可以通过创建抽象函数来创建它们，但是使用PHP+7可以定义该函数的返回类型，这使得在构建任何人都可以扩展的基类时变得容易得多。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|765865|<?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;|code-block|syntax|javascript|765866|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

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.

<pre><code>&lt;?php

abstract class FooBase {

 abstract public function FooProp(): string;
 abstract public function BarProp(): BarClass;

 public function foo() {
 return $this-&gt;FooProp();
 }

 public function bar() {
 return $this-&gt;BarProp()-&gt;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-&gt;foo() . PHP_EOL;
echo $test-&gt;bar() . PHP_EOL;
</code></pre>

Is there any way to define abstract class properties in PHP?

<pre><code>abstract class Foo_Abstract {
 abstract public $tablename;
}

class Foo extends Foo_Abstract {
 //Foo must 'implement' $property
 public $tablename = 'users'; 
}
</code></pre>

PHP abstract properties

编译器

容器

有没有办法在PHP中定义抽象类属性？abstract class Foo_Abstract {    abstract public $tablename;}class Foo extends Foo_Abstract {    //Foo must 'implement' $property    public $t...

问PHP抽象属性
EN

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问PHP抽象属性EN

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问PHP抽象属性
EN