WP_User::__isset( string $key ): bool

Source

public function __isset( $key ) {
	if ( 'id' === $key ) {
		_deprecated_argument(
			'WP_User->id',
			'2.1.0',
			sprintf(
				/* translators: %s: WP_User->ID */
				__( 'Use %s instead.' ),
				'<code>WP_User->ID</code>'
			)
		);
		$key = 'ID';
	}

	if ( isset( $this->data->$key ) ) {
		return true;
	}

	if ( isset( self::$back_compat_keys[ $key ] ) ) {
		$key = self::$back_compat_keys[ $key ];
	}

	return metadata_exists( 'user', $this->ID, $key );
}

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