How to make the foreach loop arguments variable?

Question

I have an array ($cart) that I want to process in a foreach loop either in reverse order or in normal order depending on an external switch. The code below gives the idea of what I am trying to do,

switch ($data['entire_receipt'])
    {
        case    'N':
            $foreach    =   'array_reverse($cart, true) as $line=>$item';
            break;
        case    'Y':
            $foreach    =   '$cart as $line=>$item';
            break;
        default:
            $foreach    =   'array_reverse($cart, true) as $line=>$item';
    }

    //foreach   $$foreach
    foreach ("$foreach")
    {
       // do something
    }

The code within the foreach loop is exactly the same whether processed in reverse or normal order.

The above fails on the "foreach ("foreach")" line.

Obviously I could use if statements but then I would have to duplicate the do something code, which adds maintenance complexity.

Is there a solution to this?

Thanks for your help.

Thanks for your answer. I am aware that eval is dangerous but since I am providing the code from within my script it would seem OK to use. — Hilary
– Hilary, Commented Feb 21, 2015 at 13:29
eval() can still cause problems with error reporting, it isn't just a potential security issue..... and it's totally unnecessary to use in this situation — Mark Baker
– Mark Baker, Commented Feb 21, 2015 at 13:32
eval() is not always evil -> stackoverflow.com/a/951868/1407478 I can and will not judge if eval() is inappropriate here, all I say is that it is the way to go if you want to execute code stored in a string. — davidkonrad
– davidkonrad, Commented Feb 21, 2015 at 13:38

Mark Baker · Accepted Answer · 2015-02-21 13:22:00Z

1

You can't simply create strings and expect them to be executed as code

switch ($data['entire_receipt']) {
    case 'Y' :
        $foreach = $cart;
        break;
    case 'N' :
    default  :
        $foreach = array_reverse($cart, true);
}

foreach ($foreach as $line => $item) {
   // do something
}

Note that $foreach is a copy of the $cart array, if you want to directly modify the $cart array in your foreach loop, then use the $line value as the key to $cart

answered Feb 21, 2015 at 13:22

Mark Baker

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5 Comments

davidkonrad Over a year ago

He can if he uses eval() ... But that is most of the time not very recommendable.

Mark Baker Over a year ago

Yes, if you use eval() you can, but getting in the habit of using something as dangerous as eval is a bad habit to get into, especially when it's unnecessary to do so

Mark Baker Over a year ago

eval() also has serious issues when it comes to error handling, and shouldn't be a recommended approach for any problem

Hilary Over a year ago

I decided not to use eval().

Hilary Over a year ago

Thanks Mark, I tried your solution and accepted it.

Jordi Llull · Accepted Answer · 2015-02-21 13:27:26Z

0

Yo should iterate the same variable and reverse the array if it's necessary.

if ($data['entire_receipt']) == 'N') {
    $cart = array_reverse($cart, true)
}

foreach ($cart as $line => $item) {
  // Do something
}

answered Feb 21, 2015 at 13:27

Jordi Llull

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