shell script that tests various types for "existence" using isset, empty, is_null, count, if/else, ternary, strict equality with null, … — should be easy to add/remove values and tests.

php-testing_variable_existence_results.md

Testing variable existence in php

Run the tests (code below): testing-variable-existence.php

Results Matrix

	=== null	is_null	isset	empty	if/else	ternary	count > 0
$a;	true	true		true
null	true	true		true
[ ]			true	true
0			true	true			true
''			true	true			true
1			true		true	true	true
-1			true		true	true	true
" "			true		true	true	true
"str"			true		true	true	true
[0,1]			true		true	true	true
new stdClass			true		true	true	true

Notes

Unsurprisingly:

• $a === null is identical to is_null($a)
• if/else is identical to ternary

if/else and ternary

The major difference between isset() and boolean coercion is that "" and 0 evaluate to false so if you want to guard a function like:

$a = something();
…
if ($a) {
	dostuff($a);
}

It's a good idea to know that something() returns null if either "" or 0 are valid values for dostuff().

Array items versus variables

All of the above comparisons have the same outcome whether a variable or array item is used:

foreach ($values as $v) {
   $a = $v;
   $b['key'] = $v;
   foreach ($comparsions as $func)
      $func($a) === $func($b['key']); // true for all values+tests
}

count

The last column shows results for count($a) > 0 — count() is intended for arrays and implementors of Countable and somewhat unintuitively evaluates strings, numbers, and objects to always have a count of 1.

array_key_exists

I omitted array_key_exists() from the results matrix — the main difference between isset() and array_key_exists() is the former returns true for null values.
When $a['key'] = null;:

• false === isset( $a['key'] ); // comparing the value
• true === array_key_exists( $a['key'] ); // just checks for the key

That's because isset() checks the value and array_key_exists() checks for the key. Logically if a key exists and has a non-null value then both functions will return true. It's a subtle and important difference between the two functions.

testing-variable-existence.php

#!/usr/bin/env php
<?php

/**
 *  * Responding to: http://stackoverflow.com/questions/418066/best-way-to-test-for-a-variables-existence-in-php-isset-is-clearly-broken
 *  
 * $ php path/to/this_file.php (value|v)
 *
 * arguments:
 * none      default is to show a combined table
 * (value|v) displays a table per value
 */

mb_internal_encoding("UTF-8");

$values = [
    '$a'            => $a
  , 'null'          => null
  , '[ ]'           => []
  , '0'             => 0
  , '""'            => ""
  , '1'             => 1
  , '-1'            => -1
  , '" "'           => " "
  , '"str"'         => "str"
  , '[0,1]'         => [0,1]
  , 'new stdClass ' => new stdClass
];

$array_values_source = [
  [
      'null'         => null
    , 'empty_array'  => []
    , 'zero_num'     => 0
    , 'empty_string' => ""
  ],[ // this split is arbirtray to show nesting
      'one_num'      => 1
    , '-one_num'     => -1
    , 'single_space' => " "
    , 'string'       => "str"
    , 'array'        => [0,1]
    , 'new_stdClass' => new stdClass  
  ]
];

$array_values = [
    '(missing key)'   => $array_values_source[$missing]
  , '(missing index)' => $array_values_source[99]
  , 'null'            => $array_values_source[0]['null']
  , '[ ]'             => $array_values_source[0]['empty_array']
  , '0'               => $array_values_source[0]['zero_num']
  , '""'              => $array_values_source[0]['empty_string']
  , '1'               => $array_values_source[1]['one_num']
  , '-1'              => $array_values_source[1]['-one_num']
  , '" "'             => $array_values_source[1]['single_space']
  , '"str"'           => $array_values_source[1]['string']
  , '[0,1]'           => $array_values_source[1]['array']
  , 'new stdClass'    => $array_values_source[1]['new_stdClass']
];

$tests = [
    '=== null'  => function($a){ return $a === null; }
  , 'is_null'   => function($a){ return is_null($a); }
  , 'isset'     => function($a){ return isset($a); }
  , 'empty'     => function($a){ return empty($a); }
  , 'if/else'   => function($a){ if($a){ return true; }else{ return false; } }
  , 'ternary'   => function($a){ return $a ? true : false; }
  , 'count > 0' => function($a){ return count($a) > 0; }
];

// CLI ARGUMENTS ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

if ($argv[1] === 'value' || $argv[1] === 'v')
{
  drawTablePerValue( $values, $tests );
  // drawTablePerValue( $array_values, $tests );
}
else
{
  echo "~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\n";
  echo " Values accessed from variables: \n";
  echo "~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\n";
  drawCombinedTable( $values, $tests );
  echo "~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\n";
  echo " Values accessed from array (identical results): \n";
  echo "~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\n";
  drawCombinedTable( $array_values, $tests );

  echo "~~~~~~~~~~~~~~~~~~~\n";
  echo " array_key_exists: \n";
  echo "~~~~~~~~~~~~~~~~~~~\n";
  drawArrayKeyExist();
}

// OUTPUT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

function drawCombinedTable($values, $tests)
{
  // headers
  // seed with empty space for upper-left corner
  $columns = [['', '-----']];
  // add headings (row 0) and markdown heading-pipes (row 1)
  foreach ($tests as $label => $test) {
    $columns[] = [ $label, '-----' ];
  }

  // add rows 2…n for each test(value)
  foreach ($values as $value_label => $a) {
    $i = 0;
    // value label in (col 0)
    if ($value_label === '$a') $value_label = '$a;';
    $columns[$i][] = $value_label;
    // evaluate test(value) (col 1…n)
    foreach ($tests as $test_label => $func) {
      $columns[++$i][] = $func($a) ? 'true' : '';
    }
  }

  // space each column
  $columns = array_map( 
    function($c){ return alignColumn($c); }, $columns
  );

  // draw table row by row
  $rowcount = count($columns[0]); // assume first column has correct #rows
  $colcount = count($columns);
  for ($i = 0; $i < $rowcount; $i++) {
    for ($j = 0; $j < $colcount; $j++)
      echo '| '. $columns[$j][$i] .' ';
    echo "|\n";
  }
}

function drawTablePerValue($values, $tests)
{
  foreach ($values as $table_label => $a)
  {
    // format label
    if ($table_label !== '$a')
      $table_label = '$a = '. $table_label;

    // table top + table label
    echo '+'. str_repeat('=', 8)
       .'  '. $table_label .';  '
       . str_repeat('=', 30-mb_strlen($table_label)) 
       . "+\n";

    // first row is a non-test "var_dump" item
    $testLabels = ['var_dump'];
    $results    = [captureVarDump($a)];

    // evaluate tests
    foreach ($tests as $test_label => $func) {
      $testLabels[] = $test_label;
      $results[]    = $func($a) ? 'true' : ''; // expects $func() to return boolean
    }

    // space columns
    $testLabels = alignColumn($testLabels, 'right', 20);
    $results    = alignColumn($results, 'left', 60);

    // output rows
    for ($i = 0, $len = count($results); $i < $len; $i++)
      echo '| '. $testLabels[$i] .' : '. $results[$i] . "\n"; 

    // table end
    echo "|\n";
  }
}

function drawArrayKeyExist()
{
  // setup test data
  $testdata = [
      'key for 0'     => 0
    , 'key for -1'    => -1
    , 'key for []'    => []
    , 'key for ""'    => ''
    , 0               => 'set'
    , 1               => null
    , 'key for null'  => null
  ];

  // create header
  $results = [ 
    array('key','+-+'), 
    array('value','+---+'), 
    array('array_key_exists','+--------------+'), 
    array('isset','+---+')
  ];

  // do tests
  foreach ( $testdata as $key_to_test => $z )
    doTest($results, $testdata, $key_to_test);
  doTest($results, $testdata, 2);
  doTest($results, $testdata, $blah, '($blah: doesn\'t exsist)');
  $testdata['never_set'];
  doTest($results, $testdata, 'never_set', 'never_set');

  // align columns
  $label = alignColumn($results[0], 'right');
  $vrdmp = alignColumn($results[1]);
  $ake   = alignColumn($results[2]);
  $isset = alignColumn($results[3]);

  for ($i = 0, $len = count($label); $i < $len; $i++ )
    echo '| '. $label[$i] .' : '. $ake[$i] .' : '. $isset[$i] .' : '. $vrdmp[$i] ." |\n";
}

function doTest(&$result, $test_a, $key, $label = null)
{
  if (empty($label)) $label = $key;
  if (is_string($label)) $label = "'". $label ."'";
  $result[0][] = $label;
  $result[1][] = '('. captureVarDump($test_a[$key]) .')';
  $result[2][] = array_key_exists($key, $test_a) ? 'true' : '';
  $result[3][] = isset($test_a[$key], $test_a) ? 'true' : '';
}


// TOOLBELT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

function captureVarDump($in)
{
  ob_start();
    var_dump($in);
    $capture = ob_get_clean();
  ob_end_flush();
  $capture = str_replace("\n", "", $capture); 
  $capture = str_replace("  ", " ", $capture);
  return $capture;
}

function alignColumn($strings, $position = 'left', $max = 80)
{
  $lengths = array_map( 
    function($n){ return mb_strlen($n); }, $strings
  );
  $maxlen = max($lengths);
  $maxlen = ($maxlen > $max) ? $max : $maxlen;

  $spaced = array();
  foreach ($strings as $str)
  {
    $str    = mb_substr($str, 0, $maxlen);
    $strlen = mb_strlen($str);
    $padlen = $maxlen - $strlen;
    switch ($position) {
      case 'right' : 
        $spaced[] = str_repeat(' ', $padlen) . $str; 
        break;
      case 'center' : 
        $spaced[] = str_repeat(' ', ceil($padlen/2) ) 
                  . $str 
                  . str_repeat(' ', floor($padlen/2) ); 
        break;      
      case 'left' : 
      default :
        $spaced[] = $str . str_repeat(' ', $padlen);
    }
  }

  return $spaced;
}