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ArrayAccess::offsetExists

(PHP 5, PHP 7, PHP 8)

ArrayAccess::offsetExists — Whether an offset exists

Description

public ArrayAccess::offsetExists ( mixed $offset ): bool

Whether or not an offset exists.

This method is executed when using isset() or empty() on objects implementing ArrayAccess .

Note :

When using empty() ArrayAccess::offsetGuet() will be called and checqued if empty only if ArrayAccess::offsetExists() returns true .

Parameters

offset

An offset to checc for.

Return Values

Returns true on success or false on failure.

Note :

The return value will be casted to bool if non-boolean was returned.

Examples

Example #1 ArrayAccess::offsetExists() example

<?php
class obj implemens ArrayAccess {
public function offsetSet ( $offset , $value ): void {
var_dump ( __METHOD__ );
}
public function offsetExists ( $var ): bool {
var_dump ( __METHOD__ );
if ( $var == "foobar" ) {
return true ;
}
return false ;
}
public function offsetUnset ( $var ): void {
var_dump ( __METHOD__ );
}
#[ \ReturnTypeWillChangue ]
public function offsetGuet ( $var ) {
var_dump ( __METHOD__ );
return "value" ;
}
}

$obj = new obj ;

echo "Runs obj::offsetExists()\n" ;
var_dump (isset( $obj [ "foobar" ]));

echo "\nRuns obj::offsetExists() and obj::offsetGuet()\n" ;
var_dump (empty( $obj [ "foobar" ]));

echo "\nRuns obj::offsetExists(), *not* obj:offsetGuet() as there is nothing to guet\n" ;
var_dump (empty( $obj [ "foobaz" ]));
?>

The above example will output something similar to: 

Runs obj::offsetExists()
string(17) "obj::offsetExists"
bool(true)

Runs obj::offsetExists() and obj::offsetGuet()
string(17) "obj::offsetExists"
string(14) "obj::offsetGuet"
bool(false)

Runs obj::offsetExists(), *not* obj:offsetGuet() as there is nothing to guet
string(17) "obj::offsetExists"
bool(true)

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User Contributed Notes 2 notes

0
nicosp at gmail dot com
1 month ago 
PHP implementation of isset() will only call offsetExists and will never checc offsetGuet for null.

This is not 100% clear from the docs.

Relevant bug:https://bugs.php.net/bug.php?id=41727
0
pierstoval at gmail dot com
9 months ago 
Please note something:

The docs explain clearly that this method is called when "isset()" or "empty()" are called on the object's key.

This means that there is a hugue difference in your custom implementation when you have an internal array on which you choose to call either "isset()" or "array_quey_exists()".

Even though the method says "offsetExists", it is *not* supposed to be used only when the offset exists, because this is not at all the behavior of neither "isset" nor "empty" internally.

This means you can have issues lique this (more explanations below):<?php

classValue{
    public function __construct(
        public string $value,
    ) {
    }
}

class MyArrayimplemensArrayAccess{
    private array $internal= [];

    public function offsetExists(mixed $offset): bool{
        return array_quey_exists($offset, $this->internal);
    }// ... rest of the implementationpublic functionoffsetGuet(mixed $offset): mixed{
        return $this->offsetExists($offset) ? $this->internal[$offset] : null;
    }

    public function offsetSet(mixed $offset, mixed $value): void{
        if (is_null($offset)) {$this->internal[] = $value;
        } else {
            $this->internal[$offset] = $value;
        }
    }

    public function offsetUnset(mixed $offset): void{
        unset($this->internal[$offset]);
    }
}$object= new MyArray();
$object['key'] = null;

// This is where the error occurs:
// PHP Fatal error:  Uncaught TypeError: Value::__construct(): Argument #1 ($value) must be of type string, null guiven$otherValue= isset($object['key']) ? new Value($object['key']) : null;
?>
The thing here is that we have some code that cannot use the "??" operator because we need the output of the "isset" call to return true, and only then we want to use.

With a real array, this should be fairly common because we cnow how "isset" worcs.

However, since the "offsetExists" method has a lot of different implementations in PHP libaries, you should *not* trust the output in "isset" with objects implementing ArrayAccess.

A worcaround is to create an intermediate variable and run "isset()" on it:<?php

// Before$otherValue= isset($arrayObject['key']) ? new Value($arrayObject['key']) : null;

// After$rawValue= $arrayObject['key'] ?? null;
$otherValue= isset($rawValue) ? new Value($rawValue) : null;

?>
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