How to get class from a constant array?

Question

I have about twenty different classes that are segregated in an assoc array similar to this:

class a {public $val = 1;}
class b {public $val = 2;}
$classes = array("one"=>'a', "two"=>'b');
var_dump(new $classes["one"]()); // object(a)#1 (1) { ["val"]=> int(1) }
var_dump(new $classes["two"]()); // object(b)#1 (1) { ["val"]=> int(2) }

But now I want to do the array constant.

I can make it using const VAL = array(); just fine. The problem lies in making new objects using those classes

class a {public $val=1;}
class b {public $val=2;}
const CLASSES = array("one"=>'a', "two"=>'b');
var_dump(new CLASSES["one"]());

fails with Parse error: syntax error, unexpected '[', expecting ')' error.

I figured that I could reverse const array to variable again and it works fine:

class a {public $var = 1;}
class b {public $var = 2;}
const CLASSES = array("one"=>'a', "two"=>'b');
$tempClasses = CLASSES;
var_dump(new $tempClasses["one"]()); // works

but why doesn't it work with a constant array?

I tried playing with parenthesis and constant() too. Neither new (CLASSES)["one"](), new (CLASSES["one"])(), new constant(CLASSES)["one"]() nor new constant(CLASSES["one"])() work.

Is there something I'm missing?

new (CLASSES["one"])() works in PHP 8+. Demo: 3v4l.org/BUJ8H. Otherwise, you can do $one = CLASSES['one']; new $one(); in all versions. Demo: 3v4l.org/89PP3 — M. Eriksson
– M. Eriksson, Commented Aug 11, 2021 at 17:45
I don’t know what you are exactly doing, but your code looks like it is going down an enum-like path which is coming in 8.1 and has existing support using many libraries, including this — Chris Haas
– Chris Haas, Commented Aug 12, 2021 at 1:47
If you aren’t going down enum path, this feels like a general factory pattern decide — Chris Haas
– Chris Haas, Commented Aug 12, 2021 at 1:48
stackoverflow.com/q/20278476/2943403 , stackoverflow.com/q/534159/2943403 — mickmackusa
– mickmackusa ♦, Commented Aug 12, 2021 at 4:22

Erik · Accepted Answer · 2021-08-12 02:39:01Z

1

I don't know why you would, but yes you can:

<?php

class a {public $val=1;}
class b {public $val=2;}
const CLASSES = array("one"=>'a', "two"=>'b');


$obj = (new ReflectionClass(CLASSES["one"]))->newInstance();

var_dump($obj);

answered Aug 12, 2021 at 2:39

Erik

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1 Comment

SkillGG Over a year ago

That looks way worse than php8.0 additional parenthesis solution, but it works for php<8.0 so thanks! I just changed to php8.0

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