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Date: Tue, 18 Mar 2025 15:14:09 +0000
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Subject: [PHP-DEV] Feature: Null Coalescing Variable Handling Construct
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From: php@miqrogroove.com (Robert Chapin)

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Following a brief discussion on Github today about adding operators, I 
decided a simple-looking construct is needed and is arguably a better 
solution for null coalescing comparison.

A common challenge: Need to test the value of a variable whose existence 
is unknown.

Existing solutions:

|$input = $_POST['input'] ?? 'none'; if ($input === 'yes') echo 
'success'; $_POST['input'] ??= 'none'; if ($_POST['input'] === 'yes') 
echo 'success'; |


Needed solution: What we don't have is a Variable Handling Function that 
will concisely resolve any uninitialized variable.

// Hypothetical
|if (nullc($_POST['input']) === 'yes') echo 'success'; |

The proposed construct nullc(mixed $var): mixed, will return the 
original value, or null if the variable is not declared.  This is 
consistent with the construct isset which returns false when a variable 
is assigned to null.  In this way, the two constructs isset and nullc 
will complement each other more concisely than something like the 
construct empty.


The other challenge: Null coalescing operator precedence causes 
unexpected behavior.

$test = 'off';

if ($test ?? '' === 'on') {
     // The line above is equivalent to if ($test ?? false) and will evaluate as true.
     echo 'yes';
}

if ('on' === $what ?? '') {
     // The line above is equivalent to if (('on' === $what) ?? '') and will throw a warning
}

This requires an extra set of parentheses to be workable.

$test = 'off';

if (($test ?? '') === 'on') {
     // The line above will evaluate as false.
}

These nuances were missed in the former Unary Coalesce RFC. Adding or 
not adding an operator doesn't resolve the cumbersome precedence already 
in place for ?? usage.  I was reminded of the need for a function-style 
construct while contemplating the differences between PHP's ?? operator 
and Microsoft's function Nz.  What we can do with an expression like 
nullc($test) === 'on' should be compatible with other existing operators 
and is more elegant than operators-in-parentheses or any multi-line 
statements.  This would also resolve the problem of not being able to do 
the same in a user function.

Further reading:

https://wiki.php.net/rfc/unary_null_coalescing_operator

-------------
Robert Chapin

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    <p>Following a brief discussion on Github today about adding
      operators, I decided a simple-looking construct is needed and is
      arguably a better solution for null coalescing comparison.</p>
    <p>A common challenge: Need to test the value of a variable whose
      existence is unknown.</p>
    <p>Existing solutions:</p>
    <pre class="notranslate"><code class="notranslate">$input = $_POST['input'] ?? 'none';
if ($input === 'yes') echo 'success';

$_POST['input'] ??= 'none';
if ($_POST['input'] === 'yes') echo 'success';
</code></pre>
    <p><br>
    </p>
    <p>Needed solution: What we don't have is a Variable Handling
      Function that will concisely resolve any uninitialized variable.</p>
    <pre>// Hypothetical
<code class="notranslate">if (nullc($_POST['input']) === 'yes') echo 'success';
</code></pre>
    <p></p>
    <p>The proposed construct nullc(mixed $var): mixed, will return the
      original value, or null if the variable is not declared.  This is
      consistent with the construct isset which returns false when a
      variable is assigned to null.  In this way, the two constructs
      isset and nullc will complement each other more concisely than
      something like the construct empty.</p>
    <p><br>
    </p>
    <p>The other challenge: Null coalescing operator precedence causes
      unexpected behavior.<br>
    </p>
    <pre>$test = 'off';

if ($test ?? '' === 'on') {
    // The line above is equivalent to if ($test ?? false) and will evaluate as true.
    echo 'yes';
}

if ('on' === $what ?? '') {
    // The line above is equivalent to if (('on' === $what) ?? '') and will throw a warning
}</pre>
    <p>This requires an extra set of parentheses to be workable.<br>
    </p>
    <pre>$test = 'off';

if (($test ?? '') === 'on') {
    // The line above will evaluate as false.
}</pre>
    <p>These nuances were missed in the former Unary Coalesce RFC. 
      Adding or not adding an operator doesn't resolve the cumbersome
      precedence already in place for ?? usage.  I was reminded of the
      need for a function-style construct while contemplating the
      differences between PHP's ?? operator and Microsoft's function
      Nz.  What we can do with an expression like nullc($test) === 'on'
      should be compatible with other existing operators and is more
      elegant than operators-in-parentheses or any multi-line
      statements.  This would also resolve the problem of not being able
      to do the same in a user function.<br>
    </p>
    <p>Further reading:</p>
    <p><a class="moz-txt-link-freetext" href="https://wiki.php.net/rfc/unary_null_coalescing_operator">https://wiki.php.net/rfc/unary_null_coalescing_operator</a></p>
    <pre class="moz-signature" cols="72">
-------------
Robert Chapin</pre>
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