7

Simplified example of a class:

class Table extends TableAbstract{
    protected static $tablename;

    function __construct($str){
       $this->tablename = "table_" . $str;
       $this->insert();    // abstract function
    }

}

When I've used classes like this in the past I've assigned the $tablename directly when writing the class. This time however I would like it to be decided by the constructor. But when I then call the function referencing $tablename the variable seems to be empty, when I echo the SQL.

What am I doing wrong, or could someone suggest a way to achieve what I want here?

Thanks for any comments/answers..

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  • 1
    If the class is a single instance, then a static variable is not needed. Static variables are used when you need a value to be available between multiple instances of a class. However if you are setting that value in the constructor, then each instance of the class would have the value set when the class is instantiated. When you set it to a non static property in the constructor, the non static property should still be available in each method. Commented Jun 24, 2011 at 22:21

5 Answers 5

Reset to default
8

As the property is static, access it using Table::$tablename - or alternatively self::$tablename to refer implicitly to the current class.

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2 Comments

Yes I have this already, the abstract class is functioning as expected. The problem is with assigning the variable, it seems. Because when I output the SQL, the $tablename is not there, whereas it would normally be there when I assign $tablename directly.
Yeah sorry I misunderstood, I see what you're saying now. Thanks for pointing this out.
3

when accessing a static property you need to use self::$varName instead of $this->varName. Same thing with static methods.

Edit: Just to highlight some differences between abstract and static/non-static properties, I made a small example.

<?php
abstract class A{
    public abstract function setValue($someValue);

    public function test(){
        echo '<pre>';
        var_dump($this->childProperty);
        var_dump(B::$childStatic);
        echo '</pre>';
    }
}

class B extends A{
    protected $childProperty = 'property';
    protected static $childStatic = 'static';

    public function setValue($someValue){
        $this->childProperty = $someValue;
        self::$childStatic = $someValue;
    }
}

//new instance of B
$X = new B();
//another new instance of B
$Y = new B();

//output the values
$X->test();
$Y->test();

//change the static and standard property in $X
$X->setValue("some new value");

//output the values again.
$X->test();
$Y->test();
?>

Output:

string(8) "property"
string(6) "static"

string(8) "property"
string(6) "static"

string(14) "some new value"
string(14) "some new value"

string(8) "property"
string(14) "some new value"

After you call setValue on $X, it you can see that the values of the static property change in both the instances while the non-static property changes only in that one instance.

Also, I just learned something. In a method of an abstract class trying to access a static child property, you have to specify the child class name to access the property, self:: doesn't work and throws an error.

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8 Comments

Thank you, works fine now :) I just didn't know that the self:: was also needed for static properties!
@user Why would you set a tablename that is used in a specific instance on the whole class? This way you can't create two instances with different table names, which seems absolutely pointless. Why does that property need to be static?
Well the point is I want it to vary for each instance. Doesn't it have to be static for the abstract class function which references the var using self::var ?
@user A standard property (non static) is different for each instance of the class. A static property is the same in all instances. With the abstract class, each instance of the sub class (class that implements the abstract class) will also have it's own instance of the abstract class. So methods in the abstract class can access the variables local to that instance of the sub class. In other words, don't use static for what you want.
@user I think you're really confusing class vs. instance vs. abstract. Don't use static methods or properties or self if you want individually unique instances. static/self always works on the same static class values, not on instance values.
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2

If you would google up such thing as php static you would have found that:

From PHP Manual:

Static Keyword

Static properties cannot be accessed through the object using the arrow operator ->.

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Comments

1

static properties are set on the class, not on an instance. Get rid of the static to make your $tablename a normal instance property and it should work as expected.

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1

a static member is not tied up to the instance but it's more related to the class, so you can't really reference a static member through $this. you should use self::$staticMemberName to access a static member from within a class instance.

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