Return the key of the current element

@link    http://php.net/manual/en/iterator.key.php
@return  scalar  scalar on success, or <b>NULL</b> on failure.
972292
public function key()
    {
        return isset( $this->packageNames[$this->index] )
            ? $this->packageNames[$this->index]
            : null;
    }
443930
protected function get_key_from_position() {
        $keylist = array_keys($this->userlists);
        if (isset($keylist[$this->iteratorposition])) {
            return $keylist[$this->iteratorposition];
        }

        return null;
    }
422659
public function doGetKey()
    {
        foreach ($this->data as $key => $value) {
            if ($this->value === $value) {
                return $key;
            }
        }

        return $this->default;
    }
1202648
final public function current()
    {
        if (!$this->valid()) {

            return null;
        }

        /*
         * Multiple calls to current() should be idempotent
         */
        if ($this->_lastPositionExecuted !== $this->_position) {

            $this->runToNextYieldStatement();
        }

        return $this->valid() ? $this->getLastYieldedValue() : null;
    }
1182140
public function key()
    {
        if (is_null($this->ext)) {
            $this->ext = $this->generateExt();
        }
        return $this->ext;
    }
127173
public function key()
    {
        $key = key($this->container);
        if ($this->key_type === GPBType::BOOL) {
            // PHP associative array stores bool as integer for key.
            return boolval($key);
        } elseif ($this->key_type === GPBType::STRING) {
            // PHP associative array stores int string as int for key.
            return strval($key);
        } else {
            return $key;
        }
    }
470198
public function current()
    {
        return isset($this->mappedEnums[$this->iteratorIndex])
            ? $this->valueMap[$this->mappedEnums[$this->iteratorIndex]->getConstName()]
            : null;
    }
753559
public String get(final Object key) {
    if (this._current.containsKey(key)) {
      return this._current.get(key);
    } else if (this._parent != null) {
      return this._parent.get(key);
    } else {
      return null;
    }
  }
972746
public final String key() {
    key = (key == null) ? UUID.randomUUID().toString() : key;
    return key;
  }
202892
public function key()
	{
		if( !isset( $this->____pairs ) )
			$this->getPairs();
		$keys	= array_keys( $this->____pairs );
		return $keys[$this->____cursor];
	}
150752
public function key() {
		$keys = array_keys($this->data);
		return isset($keys[$this->position]) ? $keys[$this->position] : null;
	}
671207
public function current()
	{
		if( $this->position >= $this->count() )
			return NULL;
		$keys	= array_keys( $this->pairs );
		return $this->pairs[$keys[$this->position]];
	}
1095144
public function getPrimaryKeyValue()
    {
        $primaryKey = $this->getPrimaryKey();
        if (isset($this->$primaryKey)) {
            return $this->$primaryKey;
        } else {
            return null;
        }
    }
643795
public function getKey(): string
    {
        if (null === $this->name) {
            return $this->type;
        }

        return $this->type . '#' . $this->name;
    }
1212463
public function current()
    {
        $sKey = key($this->values);

        return (true === isset($this->values[$sKey])) ? $this->values[$sKey] : null;
    }
376690
public function getPrimaryKeyValue()
    {
        $key = $this->getPrimaryKeyName();
        return isset($this->$key) ? $this->$key : null;
    }
406560
public function key()
    {
        if ( ! $this->isTranslated()) {
            return $this->key;
        }

        $parts = explode('.', $this->key);

        array_splice($parts, $this->localeIndex, 0, $this->getLocalePlaceholder());

        return trim(implode('.', $parts), '.');
    }