src/Utils/MixedStore.php
public function offsetSet($offset, $value)
    {
        if ($offset === false) {
            $this->falseValue      = $value;
            $this->falseValueIsSet = true;
        } elseif ($offset === true) {
            $this->trueValue      = $value;
            $this->trueValueIsSet = true;
        } elseif (is_int($offset) || is_string($offset)) {
            $this->standardStore[$offset] = $value;
        } elseif (is_float($offset)) {
            $this->floatStore[(string) $offset] = $value;
        } elseif (is_object($offset)) {
            $this->objectStore[$offset] = $value;
        } elseif (is_array($offset)) {
            $this->arrayKeys[]   = $offset;
            $this->arrayValues[] = $value;
        } elseif ($offset === null) {
            $this->nullValue      = $value;
            $this->nullValueIsSet = true;
        } else {
            throw new InvalidArgumentException('Unexpected offset type: ' . Utils::printSafe($offset));
        }
    }
public function offsetSet($offset, $value)
    {
        if ($offset === false) {
            $this->falseValue      = $value;
            $this->falseValueIsSet = true;
        } elseif ($offset === true) {
            $this->trueValue      = $value;
            $this->trueValueIsSet = true;
        } elseif (is_int($offset) || is_string($offset)) {
            $this->standardStore[$offset] = $value;
        } elseif (is_float($offset)) {
            $this->floatStore[(string) $offset] = $value;
        } elseif (is_object($offset)) {
            $this->objectStore[$offset] = $value;
        } elseif (is_array($offset)) {
            $this->arrayKeys[]   = $offset;
            $this->arrayValues[] = $value;
        } elseif ($offset === null) {
            $this->nullValue      = $value;
            $this->nullValueIsSet = true;
        } else {
            throw new InvalidArgumentException('Unexpected offset type: ' . Utils::printSafe($offset));
        }
    }
Offset to set

@link http://php.net/manual/en/arrayaccess.offsetset.php

@param mixed $offset <p>
The offset to assign the value to.
</p>
@param mixed $value  <p>
The value to set.
</p>

@return void