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Clarify in_array() strict comparison behavior for PHP 8.0+ #5519

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Clarify in_array() strict comparison behavior for PHP 8.0+ #5519

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b37daa4
docs: clarify in_array() strict comparison for modern PHP
joshtrichards Apr 28, 2026
a70c895
chore: linting/tidying new in-array note
joshtrichards Apr 28, 2026
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16 changes: 10 additions & 6 deletions reference/array/functions/in-array.xml
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Expand Up @@ -55,12 +55,16 @@
</para>
<note>
<para>
Prior to PHP 8.0.0, a <literal>string</literal> <parameter>needle</parameter> will match an array
value of <literal>0</literal> in non-strict mode, and vice versa. That may lead to undesireable
results. Similar edge cases exist for other types, as well. If not absolutely certain of the
types of values involved, always use the <parameter>strict</parameter> flag to avoid unexpected behavior.
</para>
</note>
Prior to PHP 8.0.0, a <literal>string</literal> <parameter>needle</parameter> would loosely match
a numeric <parameter>haystack</parameter> value of <literal>0</literal>, and vice versa.
As of PHP 8.0.0, this behavior is restricted to numeric strings. However, non-strict mode
still employs loose comparison (<literal>==</literal>), which allows for matches across
unrelated types. For example, a boolean <constant>&true;</constant> value in the
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@lacatoire lacatoire Apr 30, 2026

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unrelated types. For example, a boolean <constant>&true;</constant> value in the
unrelated types. For example, a boolean &true; value in the

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@jordikroon jordikroon May 1, 2026

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FYI; This is the cause of why CI tests fail. Because &true; is an entity that already contains a <constant>

<parameter>haystack</parameter> will match any non-empty <literal>string</literal>
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@lacatoire lacatoire Apr 30, 2026

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<parameter>haystack</parameter> will match any non-empty <literal>string</literal>
<parameter>haystack</parameter> will match any truthy <literal>string</literal>

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@lacatoire lacatoire Apr 30, 2026

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Tiny accuracy nit: "0" is technically a non-empty string but evaluates to false under PHP's loose comparison, so in_array("0", [true]) returns false (see the comparison table). "Any truthy string" would be more precise.

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@kamil-tekiela kamil-tekiela May 5, 2026

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<parameter>haystack</parameter> will match any non-empty <literal>string</literal>
<parameter>haystack</parameter> will match any non-empty <type>string</type>

<parameter>needle</parameter>. It is recommended to use the <parameter>strict</parameter>
flag to ensure type-safe results.
</para>
</note>
Comment on lines +66 to +67
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@lacatoire lacatoire Apr 30, 2026

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</para>
</note>
</para>
</note>

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@jordikroon jordikroon May 1, 2026

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This should become <simpara> as well (instead of <para>

</listitem>
</varlistentry>
</variablelist>
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