src/Primitive/Container/Container.php
public function set($key, $value)
    {
        Arr::set($this->items, $this->getKey($key), $value);

        return $this;
    }
public function set($key, $value)
    {
        Arr::set($this->items, $this->getKey($key), $value);

        return $this;
    }
Setter. Supports dot notation.

@param mixed $key
@param mixed $value
@return $this