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Fix doc bug #53117 (Assignment by reference within assignment operator) by

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breaking out the previously brief discussion of using the assignment operator
to assign by reference into its own subsection, including a reference to
by-reference assignments of new expressions being deprecated. Also updated the
References Explained section to reflect 5.3+ generating E_DEPRECATED errors in
that case, rather than E_STRICT.


git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@304605 c90b9560-bf6c-de11-be94-00142212c4b1
This commit is contained in:
Adam Harvey 2010-10-22 08:15:45 +00:00
parent 926c9caeda
commit 22434db00e
2 changed files with 70 additions and 11 deletions
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78
language/operators.xml
View file

@ -364,17 +364,75 @@ $b .= "There!"; // sets $b to "Hello There!", just like $b = $b . "There!";
Note that the assignment copies the original variable to the new
one (assignment by value), so changes to one will not affect the
other. This may also have relevance if you need to copy something
like a large array inside a tight loop. Assignment
by reference is also supported, using the <computeroutput>$var =
&amp;$othervar;</computeroutput> syntax.
'Assignment by reference' means that both variables end
up pointing at the same data, and nothing is copied anywhere.
To learn more about references, please read <link
linkend="language.references">References explained</link>. As of
PHP 5, objects are assigned by reference unless explicitly told
otherwise with the new <link linkend="language.oop5.cloning">clone</link>
keyword.
like a large array inside a tight loop.
</para>
<para>
An exception to the usual assignment by value behaviour within PHP occurs
with <type>object</type>s, which are assigned by reference in PHP 5.
Objects may be explicitly copied via the <link
linkend="language.oop5.cloning">clone</link> keyword.
</para>
<sect2 xml:id="language.operators.assignment.reference">
<title>Assignment by Reference</title>
<para>
Assignment by reference is also supported, using the
"<computeroutput>$var = &amp;$othervar;</computeroutput>" syntax.
Assignment by reference means that both variables end up pointing at the
same data, and nothing is copied anywhere.
</para>
<para>
<example>
<title>Assigning by reference</title>
<programlisting role="php">
<![CDATA[
<?php
$a = 3;
$b = &$a; // $b is a reference to $a
print "$a\n"; // prints 3
print "$b\n"; // prints 3
$a = 4; // change $a
print "$a\n"; // prints 4
print "$b\n"; // prints 4 as well, since $b is a reference to $a, which has
// been changed
?>
]]>
</programlisting>
</example>
</para>
<para>
As of PHP 5, the <link linkend="language.oop5.basic.new">new</link>
operator returns a reference automatically, so assigning the result of
<link linkend="language.oop5.basic.new">new</link> by reference results
in an <constant>E_DEPRECATED</constant> message in PHP 5.3 and later, and
an <constant>E_STRICT</constant> message in earlier versions.
</para>
<para>
For example, this code will result in a warning:
<informalexample>
<programlisting role="php">
<![CDATA[
<?php
class C {}
/* The following line generates the following error message:
* Deprecated: Assigning the return value of new by reference is deprecated in...
*/
$o = &new C;
?>
]]>
</programlisting>
</informalexample>
</para>
<para>
More information on references and their potential uses can be found in
the <link linkend="language.references">References Explained</link>
section of the manual.
</para>
</sect2>
</sect1>
<sect1 xml:id="language.operators.bitwise">

3
language/references.xml
View file

@ -105,7 +105,8 @@ $foo =& find_var($bar);
Since PHP 5, <link linkend="language.oop5.basic.new">new</link>
returns a reference automatically, so
using <literal>=&amp;</literal> in this context is deprecated and
produces an <constant>E_STRICT</constant> message.
produces an <constant>E_DEPRECATED</constant> message in PHP 5.3 and
later, and an <constant>E_STRICT</constant> message in earlier versions.
</para>
<warning>
<para>