php - passing an operator to a function - php

Is it possible to pass an operator to a function? Like this:
function operation($a, $b, $operator = +) {
return $a ($operator) $b;
}
I know I could do this by passing $operator as a string and use switch { case '+':... }. But I was just curious.

It's not possible to overload operators in php, but there is a workaround. You could e.g. pass the functions add, sub, mul and etc.
function add($a, $b) { return $a+$b; }
function sub($a, $b) { return $a-$b; }
function mul($a, $b) { return $a*$b; }
And then you function would be something like:
function operation($a, $b, $operator = add) {
return $operator($a, $b);
}

This can be done using eval function as
function calculate($a,$b,$operator)
{
eval("echo $a $operator $b ;");
}
calculate(5,6,"*");
Thanks.

Try, You cannot able to pass the operators in functions, YOU CAN USE FUNCTION NAME LIKE ADDITION, SUBTRACTION, MULTIPLICATION ... etc,
function operation($a, $b, $operator ='ADDITION') {
$operator($a, $b);
}
function ADDITION($a, $b){
return $a + $b;
}

I know you specifically mention not using a switch statement here, but I think it's important to show how this could be set up using switch statements as in my opinion it is the easiest, safest, and most convenient way to do this.
function calculate($a, $b, $operator) {
switch($operator) {
case "+":
return $a+$b;
case "-":
return $a-$b;
case "*":
return $a*$b;
case "/":
return $a/$b;
default:
//handle unrecognized operators
}
return false;
}

Related

About php7 Uniform Variable Syntax, nested functions

I'm try to solve a task which uses new functions php7 uniform variable syntax nested () support foo()() (https://wiki.php.net/rfc/uniform_variable_syntax).
I need write function test for this code:
$sum = function($a, $b) { return $a + $b; };
test(6)(2)(3)($sum); // 11
test(3)(1)($sum); // 4
test(3)(3)('pow'); // 27
I don't found any explanation for this feature. Where can I find how to use it? I see that I must return function name in function test, but how to pass argument?
Thanks all for help. It's something like this:
<?php
function test($a) {
echo '<br/>';
$arr[] = $a;
return $mf = function($b) use(&$mf, &$a, &$arr) {
if(gettype($b) == 'object') {
echo(array_reduce($arr, $b));
} elseif (gettype($b) == 'string') {
if($b == 'pow') {
echo array_reduce($arr, function ($carry, $a) {
return !empty($carry) ? pow($carry, $a) : $a;
});
}
} elseif (gettype($b) == 'integer') {
$arr[] = $b;
}
return $mf;
};
}
$sum = function($a, $b) { return $a + $b; };
test(6)(2)(3)($sum); // 11
test(3)(1)($sum); // 4
test(3)(3)('pow'); // 27
This is more about nested recursive functions, or currying, than that rfc. That rfc just enabled the syntax that supported it.
This uses recursion until you pass a callable:
function test($var) {
$values = [$var];
$function = function($callback) use (&$values, &$function) {
if (is_callable($callback)) {
return array_reduce(array_slice($values, 1), $callback, $values[0]);
}
$values[] = $callback;
return $function;
};
return $function;
}
Because your functions expect two parameters but your nesting could have unlimited parameters, it's best to use an array and array reduce.
However, since multiplication functions like pow won't work with a null initial value, you can specify the initial value as the first passed parameter from the array.

How to pass usort() a parameter?

My code:
function sortx($a, $b) {
if(!strpos($a["p_title"],'apple ipad')) {
return -1;
}
return 1;
}
usort($arr, 'sortx');`
In above function I want to pass:
$sort_text='apple ipad';
, when calling function instead of hardcoding apple ipad into strpos(). How can I accomplish that?
Call it with a closure:
$sort_text='apple ipad';
usort(
$arr,
function ($a, $b) use ($sort_text) {
if(!strpos($a["p_title"], $sort_text)) {
return -1;
}
return 1;
}
);
and you can pass additional arguments with the use clause

How to pass an additional variable into a cmp function for use with usort in php [duplicate]

This question already has answers here:
anonymous functions (lambdas, closures) in PHP 4
(2 answers)
Closed 9 years ago.
I need to order an array using usort based on a string of text that comes from a mysql call using php4.
So far I have the mysql call to get the order:
$result=mysql_query("SELECT rank from order WHERE id=1");
$row = mysql_fetch_row($result);
this gives me something like $row[0]='Alberto, Carlos, Brocephus, Edgar, Daniela';
And I have the function, which works if I hard code in an array:
function cmp($a,$b){
//$order = how do I get $row[0] in here?
$a_index = array_search($a['name'], $order);
if (!$a_index) {
$a_index = 999;
}
$b_index = array_search($b['name'], $order);
if (!$b_index) {
$b_index = 999;
}
return $a_index - $b_index;
}
usort($names,cmp);
What's the simplest way to get that string into the cmp function as an array?
You can't use a closure in PHP 4, but you can use an object.
class ArrayComparer {
var $indexedarray;
function ArrayComparer($str) {
$this->indexedarray = array_flip(explode(', ', $str));
}
function cmp($a, $b) {
$a = $a['name'];
$b = $b['name'];
$a_index = (isset($this->indexedarray[$a])) ? $this->indexedarray[$a] : 0x7fffffff;
$b_index = (isset($this->indexedarray[$b])) ? $this->indexedarray[$b] : 0x7fffffff;
return $a_index - $b_index;
}
function callback() {
return array($this, 'cmp');
}
}
Example of use:
$cmp = new ArrayComparer('Alberto, Carlos, Brocephus, Edgar, Daniela');
usort($names, $cmp->callback());
If you were in a modern version of PHP, you could simply use the use keyword like this:
function cmp($a, $b) use $your_string {
...
}
Or use a closure along with use like this:
usort(function($a, $b) use $your_string {
...
});
However, since you are working with an ancient version of PHP, you might have to resort to using a global declaration
function cmp($a, $b) {
global $your_string;
...
}

pass argument into sort function

I am using a uasort function like this:
uasort($entity_list, 'sortArray');
function sortArray($a, $b) {
if($a['fixed_column_name'] == $b['fixed_column_name']) {
return 0;
}
return ($a['fixed_column_name'] < $b['fixed_column_name']) ? -1 : 1;
}
I would like to pass a parameter to the sortArray function, like this:
uasort($entity_list, 'sortArray($arg)');
function sortArray($a, $b, $arg) {
$larg = $arg;
if($a[$larg] == $b[$larg]) {
return 0;
}
return ($a[$larg] < $b[$larg]) ? -1 : 1;
}
If you're using PHP 5.3+ (and you really should at this point in time), you can use closures:
uasort($entity_list, function ($a, $b) use ($arg) {
if ($a[$arg] == $b[$arg]) {
return 0;
}
return ($a[$arg] < $b[$arg]) ? -1 : 1;
});
Otherwise, you'll have to work around doing the same thing using global variables (oh noes!) or a class.
You could always use a class:
$sorter = new Sorter($arg);
usort($entity_list, array($sorter, "sort")); //will use $sorter->sort as callback
class Sorter {
function __construct($arg) {
$this->arg = $arg;
}
function sort($a, $b) {
// sort using $a, $b and $this->arg
}
}
Closures are nicer though ^^
Take a look at Example #4 using a closure on the usort() page of the PHP manual. The same technique can be used with all the basic sorts, including uasort()

Dynamic Comparison Operators in PHP

Is it possible, in any way, to pass comparison operators as variables to a function? I am looking at producing some convenience functions, for example (and I know this won't work):
function isAnd($var, $value, $operator = '==')
{
if(isset($var) && $var $operator $value)
return true;
}
if(isAnd(1, 1, '===')) echo 'worked';
Thanks in advance.
You can also use version_compare() function, as you can pass operator which will be used for comparison as third argument.
How about this one?
function num_cond ($var1, $op, $var2) {
switch ($op) {
case "=": return $var1 == $var2;
case "!=": return $var1 != $var2;
case ">=": return $var1 >= $var2;
case "<=": return $var1 <= $var2;
case ">": return $var1 > $var2;
case "<": return $var1 < $var2;
default: return true;
}
}
Test:
$ops = array( "=", "!=", ">=", "<=", ">", "<" );
$v1 = 1; $v2 = 5;
foreach ($ops as $op) {
if (num_cond($v1, $op, $v2)) echo "True ($v1 $op $v2)\n"; else echo "False ($v1 $op $v2)\n";
}
How about a small class:
class compare
{
function is($op1,$op2,$c)
{
$meth = array('===' => 'type_equal', '<' => 'less_than');
if($method = $meth[$c]) {
return $this->$method($op1,$op2);
}
return null; // or throw excp.
}
function type_equal($op1,$op2)
{
return $op1 === $op2;
}
function less_than($op1,$op2)
{
return $op1 < $op2;
}
}
The top answer recommends a small class, but I like a trait.
trait DynamicComparisons{
private $operatorToMethodTranslation = [
'==' => 'equal',
'===' => 'totallyEqual',
'!=' => 'notEqual',
'>' => 'greaterThan',
'<' => 'lessThan',
];
protected function is($value_a, $operation, $value_b){
if($method = $this->operatorToMethodTranslation[$operation]){
return $this->$method($value_a, $value_b);
}
throw new \Exception('Unknown Dynamic Operator.');
}
private function equal($value_a, $value_b){
return $value_a == $value_b;
}
private function totallyEqual($value_a, $value_b){
return $value_a === $value_b;
}
private function notEqual($value_a, $value_b){
return $value_a != $value_b;
}
private function greaterThan($value_a, $value_b){
return $value_a > $value_b;
}
private function lessThan($value_a, $value_b){
return $value_a < $value_b;
}
private function greaterThanOrEqual($value_a, $value_b){
return $value_a >= $value_b;
}
private function lessThanOrEqual($value_a, $value_b){
return $value_a <= $value_b;
}
}
The bigger problem is that this function is pretty pointless. Let's replace that with a real (hypothetically working) example:
function isAnd($var, $value, $operator = '==') {
return isset($var) && $var $operator $value;
}
isAnd($foo, 1, '===');
In this example $foo is not set. You'll get an error because you're trying to pass a non-existent variable ($foo) to a function (isAnd). So, you will need to test $foo for isset before calling isAnd:
isset($foo) && isAnd($foo, 1, '===');
So, any variable that ever enters the isAnd function is definitely set. You don't need to test for it inside the function. So the whole exercise is pretty pointless.
What may be confusing is that isset() and empty() don't have this limitation, i.e. you can pass a non-existent variable to them without error. The thing is though, these are not normal functions, they're special language constructs (that happen to look like functions; blame PHP). Unfortunately you can not make these kinds of constructs, parameters for your functions always need to exist.
You should just get used to writing isset($foo) && $foo === 1. With properly structured code, you can reduce this to a minimum by always declaring all variables you're going to use, which is good practice anyway.
For the dynamic operator... you'll need some form of if ... else somewhere to decide which operator to use anyway. Instead of setting the operator variable and then evaluating it, isn't it easier to do the evaluation right there?
If you absolutely insist you can use eval.
if(isset($var) && eval("return \$var $operator \$value"))
return true;
But I wouldn't recommend it.
Here is a simple solution which should work for almost all the operators
Eg.
$b = 10;
$c = '+';
$p = $a . $c. $b; // Forming a String equation
$p = eval('return '.$p.';'); // Evaluating the Equation
echo $p;
Output:
15
Another example with comparison operator:
$b = 10;
$c = '==';
$p = $a . $c. $b;
$p = eval('return '.$p.';');
echo $p;
Output:
false
Hope this helps.
As Michael Krelin suggests you could use eval - but that potentially enables a lot of code injection attacks.
You can't substitute a variable for an operator - but you can substitute a variable for a function:
function is_equal($a, $b) {
return $a==$b;
}
function is_same($a, $b) {
return $a===$b;
}
function is_greater_than($a, $b)
....
$compare='is_equal';
if ($compare($a, $b)) {
....
C.
As far as I know it is not possible and since there is no reference about callback on operators in PHP documentation,
http://www.php.net/manual/en/language.operators.php
instead of using eval, I would redefine each operators in global functions and use php callbacks
How do I implement a callback in PHP?
$a = 4;
eval('$condition=($a == 4)?true:false;');
if($condition){ echo "Yes"; }else{ echo "No"; }
No, it's impossible.
You can use conditional operators instead, but it will be much,much better if you redesign your application to make such a dynamic comparison unnecessary.

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