Undefined property in dynamic variable of a PHP class

Question

I am trying to get a dynamic variable value in a PHP class but not sure how to do this. Here's my code:

<?php
class Test
{
    public $type = "added";

    public $date_added;

    public function set_status()
    {
        $this->date_added = "Pass";
    }

    public function get_status()
    {
        echo $this->date_{$type};
    }
}

$test = new Test();
$test->set_status();
$test->get_status();
?>

I am getting following error:

Notice: Undefined property: Test::$date_ in...

Notice: Undefined variable: type in ...

If I write echo $this->date_added; in place of echo $this->date_{$type}; then I get output "Pass".

How to fix it and do it properly?

Kevin · Accepted Answer · 2020-02-12 03:45:55Z

2

Since you're using variable variables, put them in quotes, then concatenate:

echo $this->{'date_' . $this->type};
                    // not $type, use `$this->` since it's part of your properties

Or using via formatted string (double quotes will work as well):

echo $this->{"date_{$this->type}"};

answered Feb 12, 2020 at 3:45

Kevin

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2 Comments

Sachin Over a year ago

So it is called variable of a variable or dynamic variable? Single quotes will not work in your second syntax?

Kevin Over a year ago

@Sachin yes, that's what PHP calls it. if you use single quotes on the second version, you'll get the literal date_{$this->type}. you need to interpolate the value from $this->type to get date_added, and via double quotes it is possible

Marmik Patel · Accepted Answer · 2020-02-12 04:05:38Z

1

<?php
class Test
{
    public $type = "added";

    public $date_added;

    public function set_status()
    {
        $this->date_added = "Pass";
    }

    public function get_status()
    {
        echo $this->{'date_' . $this->type};
    }
}

$test = new Test();
$test->set_status();
$test->get_status();
?>

answered Feb 12, 2020 at 4:05

Marmik Patel

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Comments

Atiqur · Accepted Answer · 2020-02-12 04:39:08Z

0

You can do it multiple ways, date_{$type} is not valid expression and to acccess the class property you have to use this keyword .

class Test
{
    public $type = "added";

    public $date_added;

    public function set_status()
    {
        $this->date_added = "Pass";
    }

    public function get_status()
    {
        $prop = 'date_'.$this->type;

        echo $this->{'date_'.$this->type}; # one way to do it
        echo $this->$prop;                  # another way to do it
        echo $this->{"date_{$this->type}"}; # another way to do it
    }
}

$test = new Test();
$test->set_status();
$test->get_status();

answered Feb 12, 2020 at 4:39

Atiqur

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3 Comments

Sachin Over a year ago

What is $prop? Please explain.

Atiqur Over a year ago

$prop is just another variable that holds the actual property value as string, this is a good practice when you have to do some calculation/concatenation/operation to make the final property name like here. $prop = 'date_'.$this->type;

Sachin Over a year ago

OK, I got it. Thanks.

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