Access a static variable using a variable - PHP

Question

I have this PHP code block -:

$visible_to = 'private';
$icon = array('public' => 'ICON_GLOBE', 'private' => 'ICON_LOCK');
echo TbHtml::$icon[$visible_to];

But running this prints -: Access to undeclared static property: TbHtml::$icon.

Whats the problem with my code? Thanks :)

Heres the TbHtml class -:

class TbHtml
{
     const ICON_GLOBE = 'Its a globe';
     const ICON_LOCK = 'Its a lock';
}

You need to show us the class TbHtml in order for us to figure that out. — Damien Black
– Damien Black, Commented Jan 14, 2014 at 18:08
The problem with your code is that you are trying to access an undeclared static property. — kero
– kero, Commented Jan 14, 2014 at 18:09
I want my code to get the value of $icon['public'] & not take it as a simple string. — sanchitkhanna26
– sanchitkhanna26, Commented Jan 14, 2014 at 18:15

Jason Fingar · Accepted Answer · 2014-01-14 18:22:56Z

2

People are down-voting Mubo, but his answer is closest to being correct in my opinion. You shouldn't be trying to call class constants using dynamic parts. Why not just do:

$visible_to = 'private';
$icon = array('public' => TbHtml::ICON_GLOBE, 'private' => TbHtml::ICON_LOCK);
echo $icon[$visible_to];

answered Jan 14, 2014 at 18:22

Jason Fingar

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1 Comment

Mike Brant Over a year ago

A very simple and effective approach. The only downside to this might be that the calling code is stilled tightly coupled to the class as it needs to understand that static constant names. If you want to decouple this, you might consider exposing a static method that accepts "visibility" value and returns the proper static property value.

Mike Brant · Accepted Answer · 2014-01-14 18:24:22Z

0

You can utilize get_class_vars() to get to this information:

$class_vars = get_class_vars('TbHtml');
$desired_value = $class_vars[$icon[$visible_to]];

I would however suggest exposing a static method in your class if you class needs to understand public vs. private:

public static function get_icon_by_visibility($visibility = 'public') {
    if ($visibility === 'public') {
        return self::ICON_GLOBE;
    } else if ($visibility === 'private') {
        return self::ICON_LOCK;
    } else {
        throw new Exception('Invalid paramater passed.');
    }
}

// usage
echo TbHtml::get_icon_by_visibility($visible_to);

edited Jan 14, 2014 at 18:24

answered Jan 14, 2014 at 18:18

Mike Brant

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Comments

Damien Black · Accepted Answer · 2014-01-14 18:25:46Z

0

You need to do this:

echo TbHtml::${$icon[$visible_to]};

Two dollar signs so that you get the value of $icon[$visible_to] and use that as the variable name.

However, such trickery is bad code. It would be better practice if you did something like this, where you store the icons in an array so that you don't save the variable NAMES in the $icon array, but rather their KEYS:

class TbHtml
{
     const ICONS = array('GLOBE'=>'Its a globe', 'LOCK'=>'Its a lock')
}

and

$visible_to = 'private';
$icon = array('public' => 'GLOBE', 'private' => 'LOCK');
$visible_to_icon = $icon[$visible_to];
echo TbHtml::$globe[$visible_to_icon];

edited Jan 14, 2014 at 18:25

answered Jan 14, 2014 at 18:13

Damien Black

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4 Comments

Jason Fingar Over a year ago

This answer may be technically correct, but variable variables ($$) are very poor practice and should be discouraged

qwertynl Over a year ago

So just do ${$icon[$visible_to]}? @JasonFingar

sanchitkhanna26 Over a year ago

Doing TbHtml::$$icon[$visible_to]; results in Access to undeclared static property: TbHtml::$ICON_GLOBE. Your second option may be correct. But isn't there any way out which doesn't requires a change in the TbHtml class.

Damien Black Over a year ago

Must be using an odd order of operations, use the comment above, I'll update. Although, I just tested it and it should work.

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