Variable Operators in PHP

Question

Given this example, how would I return the result of the equation rather than the equation itself as a string?

$operator = '+';
foreach($resultSet as $item){
    $result = $item[$this->orderField] . $operator . 1;
    echo $result;
}

Answer 1

You can use eval(), but it's generally a bad idea, since it's a major potential security hole (be careful you're not allowing visitors to run arbitrary code!).

It can also result in hard to maintain code.

Answer 2

Use the eval function of PHP: http://php.net/manual/en/function.eval.php

$operator = '+';
foreach($resultSet as $item){
    $result = $item[$this->orderField] . $operator . 1;
    eval("\$result = \"$result\";");
    echo $result;
}

Answer 3

Quick answer is eval(). However, in this precise example I would just hard-code the possible operations:

<?php

$operator = '+';
foreach($resultSet as $item){
    switch($operator){
        case '+':
            $result = $item[$this->orderField] + 1;
            break;
    }
    echo $result;
}

?>

Answer 4

To achieve exactly that, you can use create_function

$operator = '+';
$func = create_function('$a,$b', "return \$a $operator \$b;");
foreach($resultSet as $item){
    $result = $func($item, 1);
    echo $result;
}

A cleaner solution is possible with lambdas (php5.3 required)

$func = function($a, $b) { return $a + $b; };
foreach($resultSet as $item){
    $result = $func($item, 1);
    echo $result;
}

See also array_sum, array_reduce

Advanced example with array_reduce and lambdas

$ary = array(
    array('foo' => 1, 'bar' => 91),
    array('foo' => 2, 'bar' => 92),
    array('foo' => 3, 'bar' => 93),
    array('foo' => 4, 'bar' => 94),
    array('foo' => 5, 'bar' => 95),
);

$sumOfFoos = array_reduce($ary, 
    function($val, $item) { return $val + $item['foo']; } 
);
$sumOfBars = array_reduce($ary, 
    function($val, $item) { return $val + $item['bar']; } 
);

The main point is, that instead of 'variable operators' (which is not possible in php), you should rather use variable functions (which is possible and much more flexible).

Answer 5

You could make functions that wrap the operators, or for simplicity just use the bc extension:

$operator = '+';
$operators = array(
  '+' => 'bcadd',
  '-' => 'bcsub',
  '*' => 'bcmul',
  '/' => 'bcdiv'
);

foreach($resultSet as $item){
    $result = call_user_func($operators[$operator], $item[$this->orderField], 1);
    echo $result;
}