src/Bag.php
public function set($key, $value)
    {
        Deprecated::method(1.1, MutableBag::class);

        $this->items[$key] = $value;
    }
public function set($key, $value)
    {
        Deprecated::method(1.1, MutableBag::class);

        $this->items[$key] = $value;
    }
Sets a item by key.

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

@deprecated since 1.1 and will be removed in 2.0. Use {@see MutableBag} instead.