src/Flash.php
public function load(string $key, callable $callback)
    {
        if (!$this->has($key)) {
            $this->set($key, $callback($key));
        }

        return $this->get($key);
    }
public function load(string $key, callable $callback)
    {
        if (!$this->has($key)) {
            $this->set($key, $callback($key));
        }

        return $this->get($key);
    }
Read the value associated with the specified key or associate
the specified key with the value returned by invoking the callback.

@param string $key Key
@param callable $callback Callback

@return mixed