ArrayAccess::offsetExists

(PHP 5, PHP 7, PHP 8)

ArrayAccess::offsetExistsオフセットが存在するかどうか

説明

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

オフセットが存在するかどうかを返します。

このメソッドが実行されるのは、ArrayAccess を実装したオブジェクト上で isset() あるいは empty() を使用した場合です。

注意:

empty() を使用すると ArrayAccess::offsetGet() がコールされ、ArrayAccess::offsetExists()true を返すかどうかで空かどうかを判断します。

パラメータ

offset

調べたいオフセット。

戻り値

成功した場合に true を、失敗した場合に false を返します。

注意:

非 boolean 値が返された場合は bool にキャストして返します。

例1 ArrayAccess::offsetExists() の例

<?php
class obj implements 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__);
}
#[
\ReturnTypeWillChange]
public function
offsetGet($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::offsetGet()\n";
var_dump(empty($obj["foobar"]));

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

上の例の出力は、 たとえば以下のようになります。

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

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

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

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User Contributed Notes 1 note

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pierstoval at gmail dot com
15 days 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 huge difference in your custom implementation when you have an internal array on which you choose to call either "isset()" or "array_key_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 like this (more explanations below):

<?php

class Value {
public function
__construct(
public
string $value,
) {
}
}

class
MyArray implements ArrayAccess {
private array
$internal = [];

public function
offsetExists(mixed $offset): bool
{
return
array_key_exists($offset, $this->internal);
}

// ... rest of the implementation
public function offsetGet(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 given
$otherValue = isset($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 know how "isset" works.

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 workaround 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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