PHP RFC: standard built-in is_empty() function

• Version: 0.1
• Date: 2023-10-30
• Author: Alessandro Rosa, alessandro.a.rosa@gmail.com
• Status: Under Discussion
• First Published at: http://wiki.php.net/rfc/empty_function

So far the goal of the standard function `empty' is, according to the official documentation, to “determine whether a variable is empty”. There are kinds of flaws that should be settled, in my viewpoint:

1) the semantics: the function name is ambiguous about the action, that is, it is not clear whether the goal of empty() function should consist of testing the `emptiness' of input variable or return an empty version of the input variable.

2) the behavior. The only two issues come from inputing no variable or managing the false/true constant values. I resumed the behavior here below:

echo "built-in function `empty'<br/>";
echo "null value: ".( empty( null ) ? "Yes" : "No" )."<br/>";
echo "undeclared var : ".( empty( $i ) ? "Yes" : "No" )."<br/>";
//echo "empty input : ".( empty() ? "Yes" : "No" )."<br/>"; //empty input var will let code crash
echo "empty string : ".( empty( "" ) ? "Yes" : "No" )."<br/>";
echo "empty array : ".( empty( [] ) ? "Yes" : "No" )."<br/>";
$i = 1;
echo "boolean false : ".( empty( false ) ? "Yes" : "No" )."<br/>"; // expected value : 1
echo "boolean true : ".( empty( true ) ? "Yes" : "No" )."<br/>"; // expected value : 1
echo "declared var : ".( empty( $i ) ? "Yes" : "No" )."<br/>"; // expected value : 1
echo "non-empty string : ".( empty( "something" ) ? "Yes" : "No" )."<br/>"; // expected value : 1
echo "non empty array : ".( empty( [10] ) ? "Yes" : "No" )."<br/>"; // expected value : 1

First, the `empty' name shall be adequated to the `is_' family of php built-in functions (is_null, is_bool, is_string, is_array, ...). Hence I propose `is_empty'. The return value will be true for emptiness and false otherwise. If the input variable is not empty would throw an error.

Second, I implemented the following version which fixes the above two flaws:

function is_empty( $input = null )
{
	$ser = @serialize( $input );
	if ( preg_match( "/^N;$/i", $ser ) === 1 ) return 1;
	if ( preg_match( "/^b\:[01]\;?$/i", $ser ) === 1 ) return 1;
	return preg_match( "/0\:(\{\}|\[\]|\"\")\;?$/i", $ser ) === 1 ? 1 : 0;
}

I resorted to the `serialize' built-in function just to show how it should work. This is just an escamotage coded in PHP for obtaining a formal basis and checking input variable consistence in the examples below. However, I presume that the internal C-version would approach the emptiness test in better ways that PHP is not able to perform. Hence note that I suppressed warnings in order to let this function run throughout the following tests, that also cover undefined variables:

echo "null value: ".is_empty( null )."<br/>"; // expected return value : 0
echo "undeclared var : ".is_empty( $i )."<br/>"; // expected return value : 0
echo "empty input : ".is_empt()."<br/>"; // expected return value : 0
echo "empty string : ".is_empty( "" )."<br/>"; // expected return value : 0
echo "empty array : ".is_empty( [] )."<br/>"; // expected return value : 0
echo "<br/><br/>";

$i = 1;
echo "boolean false : ".is_empty( false )."<br/>"; // expected return value : 1
echo "boolean true : ".is_empty( true )."<br/>"; // expected return value : 1
echo "declared var : ".is_empty( $i )."<br/>"; // expected return value : 1
echo "non-empty string : ".is_empty( "something" )."<br/>"; // expected return value : 1
echo "non empty array : ".is_empty( [10] )."<br/>"; // expected return value : 1

Code works correctly and it can be also finely read.

next PHP 8.(x+2) [suggested] The status of empty() function shall be set to `deprecated'. The new is_empty() function will co-live with the older one until the latter will be definitely superseeded after 2 versions (suggest deadline) from the official embedding in the standard library.

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Please explain how you have verified your RFC's compatibility with opcache.

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Just the current nomenclature of standard built-in empty() function.

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We will probably vote for or against adding these functions. This requires 2/3 majority.

Links to any external patches and tests go here.

If there is no patch, make it clear who will create a patch, or whether a volunteer to help with implementation is needed.

Make it clear if the patch is intended to be the final patch, or is just a prototype.

For changes affecting the core language, you should also provide a patch for the language specification.

Refer to the above code.

No refs or links

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