private function getAvailableVersions()
    {
        if (!isset($this->availableVersions)) {
            $this->availableVersions = [];
            foreach ($this->getManifest() as $key => $item) {
                if ($missing = array_diff(self::$requiredKeys, array_keys($item))) {
                    throw new \RuntimeException(sprintf(
                        'Manifest item %s missing required key(s): %s',
                        $key,
                        implode(',', $missing)
                    ));
                }
                $this->availableVersions[$item['version']] = $item;
            }
        }

        return $this->availableVersions;
    }
private function getAvailableVersions()
    {
        if (!isset($this->availableVersions)) {
            $this->availableVersions = [];
            foreach ($this->getManifest() as $key => $item) {
                if ($missing = array_diff(self::$requiredKeys, array_keys($item))) {
                    throw new \RuntimeException(sprintf(
                        'Manifest item %s missing required key(s): %s',
                        $key,
                        implode(',', $missing)
                    ));
                }
                $this->availableVersions[$item['version']] = $item;
            }
        }

        return $this->availableVersions;
    }
private function getAvailableVersions ( ) { if ( ! isset ( $ this -> availableVersions ) ) { $ this -> availableVersions = [ ] ; foreach ( $ this -> getManifest ( ) as $ key => $ item ) { if ( $ missing = array_diff ( self :: $ requiredKeys , array_keys ( $ item ) ) ) { throw new \ RuntimeException ( sprintf ( 'Manifest item %s missing required key(s): %s' , $ key , implode ( ',' , $ missing ) ) ) ; } $ this -> availableVersions [ $ item [ 'version' ] ] = $ item ; } } return $ this -> availableVersions ; }
Get available versions to update to.

@return array
An array keyed by the version name, whose elements are arrays
containing version information ('version', 'sha256', and 'url').
Get available versions to update to .