cvs: phpdoc /en/language variables.xml

mfischer Sun Jun 9 19:15:30 2002 EDT Modified files: /phpdoc/en/language variables.xml Log: - Document the behaviour of 'static' and 'global' when using references, closes $12454 (and probably a few others too). Index: phpdoc/en/language/variables.xml diff -u phpdoc/en/language/variables.xml:1.46 phpdoc/en/language/variables.xml:1.47 --- phpdoc/en/language/variables.xml:1.46 Mon Apr 29 04:41:49 2002 +++ phpdoc/en/language/variables.xml Sun Jun 9 19:15:26 2002 @@ -1,5 +1,5 @@ <?xml version="1.0" encoding="iso-8859-1"?> -<!-- $Revision: 1.46 $ --> +<!-- $Revision: 1.47 $ --> <chapter id="language.variables"> <title>Variables</title> @@ -452,6 +452,111 @@ ]]> </programlisting> </informalexample> + + <simpara> + The Zend Engine 1, driving <literal>PHP4</literal>, implements the + <literal>static</literal> and <literal>global</literal> modifier for + variables in terms of references. For example, a true global variable + imported inside a function scope with the <literal>global</literal> + statement actually creates a reference to the global variable. This can + lead to unexpected behaviour which the following example addresses: + </simpara> + + <informalexample> + <programlisting role="php"> +<![CDATA[ +function test_global_ref() { + global $obj; + $obj = &new stdclass; +} + +function test_global_noref() { + global $obj; + $obj = new stdclass; +} + +test_global_ref(); +var_dump($obj); +test_global_noref(); +var_dump($obj); +]]> + </programlisting> + </informalexample> + + <simpara> + Executing this example will result in the following output: + </simpara> + + <screen> +NULL +object(stdClass)(0) { +} + </screen> + + <simpara> + A similar behaviour applies to the <literal>static</literal> statement. + References are not stored statically: + </simpara> + + <informalexample> + <programlisting role="php"> +<![CDATA[ +function &get_instance_ref() { + static $obj; + + echo "Static object: "; + var_dump($obj); + if (!isset($obj)) { + // Assign a reference to the static variable + $obj = &new stdclass; + } + $obj->property++; + return $obj; +} + +function &get_instance_noref() { + static $obj; + + echo "Static object: "; + var_dump($obj); + if (!isset($obj)) { + // Assign the object to the static variable + $obj = new stdclass; + } + $obj->property++; + return $obj; +} + +$obj1 = get_instance_ref(); +$still_obj1 = get_instance_ref(); +echo "\n"; +$obj2 = get_instance_noref(); +$still_obj2 = get_instance_noref(); +]]> + </programlisting> + </informalexample> + + <simpara> + Executing this example will result in the following output: + </simpara> + + <screen> +Static object: NULL +Static object: NULL + +Static object: NULL +Static object: object(stdClass)(1) { + ["property"]=> + int(1) +} + </screen> + + <simpara> + This example demonstrates that when assigning a reference to a static + variable, it's not <emphasis>remembered</emphasis> when you call the + <literal>&amp;get_instance_ref()</literal> function a second time. + </simpara> + </sect1>