public function set(string $key, $value): self
    {
        $this->collection[$key] = $value;

        return $this;
    }
public function set(string $key, $value): self
    {
        $this->collection[$key] = $value;

        return $this;
    }
public function set ( string $ key , $ value ) : self { $ this -> collection [ $ key ] = $ value ; return $ this ; }
Set a new item into the collection.

@param string $key   The key
@param mixed  $value The value

@return self
Set a new item into the collection .