Fallthrough variable assignment in PHP?

Question

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Coalesce function for PHP?

I'm not sure what this is normally called, but I hope the title communicates well enough. What I have is a handful of variables some of which might be null.

I want to do:

$a = $b || $c || $d;

Where $a ends up being = to the first non-null variable.

Are you trying to assign the contents of b OR c OR d to a :\? — theBigChalk, Jun 16 '12 at 00:25
Wrong language for this. It would work in Ruby or JavaScript. In PHP, AFAIK, you need to go with the trinary operator and write `$b !== null ? $b : ($c !== null ? $c : $d)` — Amadan, Jun 16 '12 at 00:26
See also: http://stackoverflow.com/questions/1013493/coalesce-function-for-php — Wrikken, Jun 16 '12 at 00:34

Niet the Dark Absol · Answer 1 · 2012-06-16T00:32:36.387

4

To my knowledge, PHP doesn't support this in the same way JavaScript does.

You can, however do something like this:

$a = $b ? $b : ($c ? $c : $d);

A more general solution:

function fallthrough($arr) {
    //$arr should be an array of possible values. The first non-null value is returned
    do $a = array_shift($arr);
    while($a === null && $arr);
    return $a;
}

edited Jun 16 '12 at 00:32

answered Jun 16 '12 at 00:26

Niet the Dark Absol

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So, what would be the best way to do this in PHP? Clearly I can't just nest ternary operators as that will get insane with more variables. Do I just have a big if elseif block? – Joren Jun 16 '12 at 00:27
Careful - if `$b` is `"0"`, it will fall through. To be more precise, it will fall through on any falsy value. If you really need only `null` to fall through, you need to explicitly test. – Amadan Jun 16 '12 at 00:29
What you could do is define a function. I'll edit my answer with a solution. – Niet the Dark Absol Jun 16 '12 at 00:30

score 3 · Answer 2 · answered Jun 16 '12 at 00:32

3

<?php
$a = 0;
$b = false;
$c = true; //should become this
$d = '1';
$e =  $a ?: $b ?: $c ?: $d;
var_dump($e);
//bool(true)

//should be '1' if order is different
$e =  $a ?: $b ?: $d ?: $c;
var_dump($e);
//string(1) "1"

... however ?: is kinda new, you will confuse your colleagues / fellow coders.

answered Jun 16 '12 at 00:32

Wrikken

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Oh, and as stated: fails on all falsy values, not just NULL. – Wrikken Jun 16 '12 at 00:33

Joe Dyndale · Answer 3 · 2012-06-16T00:48:00.747

I don't think that's possible. I think you'd have to use some other, more laborious, way. I.e. make an array of the variables, iterate through it until you find a non-null value and break the loop, like so:

$vars = array("b" => $b, "c" => $c, "d" => $d);

foreach($vars as $var) {
   if($var != null) {
      $a = $var;
      break;
   }
}

Well, like some other answers here say, you can use the shorthand way of writing this, but writing readable code is important too. The above code is pretty readable.

Fallthrough variable assignment in PHP?

3 Answers3