[doc-en] master: Rewrite example on for page (#5752)

Author: Kamil Tekiela (kamil-tekiela) Committer: GitHub (web-flow) Pusher: kamil-tekiela Date: 2026-09-07T17:36:01+01:00 Commit: https://github.com/php/doc-en/commit/8c273ad6577a6b4d6d3adea73502a4516ca2fe0c Raw diff: https://github.com/php/doc-en/commit/8c273ad6577a6b4d6d3adea73502a4516ca2fe0c.diff Rewrite example on for page (#5752) Co-authored-by: Louis-Arnaud <la.catoire@gmail.com> Changed paths: M language/control-structures/for.xml Diff: diff --git a/language/control-structures/for.xml b/language/control-structures/for.xml index b3fe2b350578..9862411e3f02 100644 --- a/language/control-structures/for.xml +++ b/language/control-structures/for.xml @@ -142,97 +142,61 @@ endfor; </informalexample> </para> <simpara> - It's common for many users to iterate through arrays like in the - example below. + Expressions <varname>expr2</varname> and <varname>expr3</varname> are + evaluated every iteration. It's advisable to use simple expressions in these + places to avoid performance issues. For example, if the number of iterations + is known in advance, it is better to use a variable instead of a function call + in <varname>expr2</varname>: </simpara> <para> <informalexample> - <programlisting role="php"> + <programlisting role="php" annotations="non-interactive"> <![CDATA[ <?php -/* - * This is an array with some data we want to modify - * when running through the for loop. - */ -$people = array( - array('name' => 'Kalle', 'salt' => 856412), - array('name' => 'Pierre', 'salt' => 215863) -); -for($i = 0; $i < count($people); ++$i) { - $people[$i]['salt'] = random_int(100000, 999999); +$people = ['Kalle', 'Pierre']; + +// Bad practice: calling a function on every iteration +for($i = 0; $i < getIterationCount($people); ++$i) { + $people[$i] .= ' is cool'; } -var_dump($people); -]]> - </programlisting> - &example.outputs.similar; - <screen> -<![CDATA[ -array(2) { - [0]=> - array(2) { - ["name"]=> - string(5) "Kalle" - ["salt"]=> - int(454478) - } - [1]=> - array(2) { - ["name"]=> - string(6) "Pierre" - ["salt"]=> - int(776978) - } + +// Good practice: storing the count in a variable +for($i = 0, $peopleCount = getIterationCount($people); $i < $peopleCount; ++$i) { + $people[$i] .= ' is cool'; } + ]]> - </screen> + </programlisting> </informalexample> </para> <simpara> - The above code can be slow, because the array size is fetched on - every iteration. Since the size never changes, the loop can be easily - optimized by using an intermediate variable to store the size instead - of repeatedly calling <function>count</function>: + In the example above, the function is called on every iteration of the + first loop, even though it always returns the same value. Storing that + value in a variable, as the second loop does, calls the function once. + Note that the number of iterations is then fixed: if the array is + modified inside the loop, the stored value no longer reflects its size. </simpara> - <para> - <informalexample> - <programlisting role="php"> -<![CDATA[ -<?php -$people = array( - array('name' => 'Kalle', 'salt' => 856412), - array('name' => 'Pierre', 'salt' => 215863) -); -for($i = 0, $size = count($people); $i < $size; ++$i) { - $people[$i]['salt'] = random_int(100000, 999999); -} -var_dump($people); -]]> - </programlisting> - &example.outputs.similar; - <screen> -<![CDATA[ -array(2) { - [0]=> - array(2) { - ["name"]=> - string(5) "Kalle" - ["salt"]=> - int(454478) - } - [1]=> - array(2) { - ["name"]=> - string(6) "Pierre" - ["salt"]=> - int(776978) - } -} -]]> - </screen> - </informalexample> - </para> + <note> + <simpara> + The size of an <type>array</type> is stored with the array, which means that + calling the built-in function <function>count</function> does not require + counting the elements and does not cause performance issues. This does not + apply to <constant>COUNT_RECURSIVE</constant>, which walks the whole array. + Care should also be taken when using <function>count</function> on objects + implementing <interfacename>Countable</interfacename>, as such calls can be + more expensive. + </simpara> + </note> + + <note> + <simpara> + The <literal>for</literal> loop is not the recommended way to + iterate over arrays. The &foreach; loop is specifically + designed for this purpose and is usually more convenient. + </simpara> + </note> </sect1> <!-- Keep this comment at the end of the file