Default value for an associative array in PHP, if key not present-CodePudding

Note: I have already read Function to set default value of associative array if the key is not present and Default values for Associative array in PHP.

Let's say:

$a = array('foo' => '123');
$b = $a['bar'];       // PHP Notice:  Undefined index: bar

I'd like to have an empty string by default "" if the key is not present, instead of a PHP Notice.

I know the solutions would be to do:

$b = isset($a['bar']) ? $a['bar'] : "";
// or, since PHP 5.3:
$b = $a['bar'] ?: "";      // but this still produces a "PHP Notice"!

Is there a way to avoid the ?: "" and directly have:

$b = $a['bar'];

get "" with no Notice?

Note: this exists in Python with:

import collections
d = collections.defaultdict(str)
print(d['bar'])   # empty string, no error

CodePudding user response：

No. PHP arrays don't work that way.

What you can do to achieve a similar simplicity is use a class. Then you can write,

$a = new FakeArray([ 'foo' => '123' ]);

$a->setDefault('baz');

$b = $a->bar; // $b is now 'baz'.
$c = $a->foo; // $c is now '123'.

and have $a return a default value of your choice using a magic getter.

I would have thought that extending ArrayObject would have come very close to what you wanted:

class FakeArray extends ArrayObject {
    ...
    public function __get($key) {
         return $this->default;
    }
}

but while $a['foo'] = 'bar' does store the value, actually even accessing a nonexistent property now triggers an Index notice:

$b = $a->baz;

PHP Notice:  Undefined index: baz in ./test.php ...

So, the ArrayObject actually behaves worse than a StdClass.

CodePudding user response：

I'd like to submit another solution using array ArrayObject as stated above

This extends the class and slightly tweaks the offsetGet behavior to always return an empty string

the parent:: statement here invokes the function of the extended class

class MyArrayObject extends ArrayObject
{
   function offsetGet( $key )
   {
     return parent::offsetExists( $key ) ? parent::offsetGet( $key ) : '';
   }
}

$myArray = new MyArrayObject( array( 'foo' => '123') );

var_dump( $myArray['foo'] ); // '123' provided string
var_dump( $myArray['bar'] ); // '' our new default
var_dump( isset( $myArray['foo'] ) ); // true
var_dump( isset( $myArray['bar'] ) ); // false

foreach( $myArray as $key )
{
    var_dump( $key ); // only one iteration of '123'
}

var_dump( is_array( $myArray ) ); // false unfortunately
var_dump( is_iterable( $myArray ) ); // true however

var_dump( array_merge( array(), $myArray ) ); // will fail
var_dump( array_merge( array(), (array) $myArray ) ); // will work

and finally

$myArray['bar'] = '456'; // now if we set bar
var_dump( $myArray['bar'] ); // '456' new value
var_dump( isset( $myArray['bar'] ) ); // now true

as a suggestion from @miken32 to set a default value

class MyArrayObject extends ArrayObject
{
    protected $default;
    public function __construct($array = [], $default = null, $flags = 0, $iteratorClass = "ArrayIterator")
    {
        parent::__construct( $array, $flags, $iteratorClass );
        $this->default = $default;
    }
    function offsetGet( $key )
    {
        return parent::offsetExists( $key ) ? parent::offsetGet( $key ) : $this->default;
    }
}

you can set a default value via

$myArray = new MyArrayObject( array( 'foo' => '123'), 'mydefault' );

CodePudding user response：

You'd have to pre-populate your array with your defaults or create a object class as stated to handle the default response.

$array = array('foo' => '123')   array('foo' => '', 'bar' => '');

var_dump( $array );

array(2) {
  ["foo"]=>string(3) "123"
  ["bar"]=> string(0) ""
}

CodePudding user response：

1 step - add this function:

function getIfIsset(array $array, string $key)
{
    return $array[$key] ?? '';
}

2 step - use this:

echo getIfIsset($mayArray, 'bar');

CodePudding user response：

You can use this method @ before variable with key:

echo @$a['bar'];