Result.php

class Result
{
    public $value;
    public $error;

    private function __construct($value, $error = null)
    {
        $this->value = $value;
        $this->error = $error;
    }

    public static function error(string $msg): Result
    {
        return new Result(null, $msg);
    }

    public static function success($value): Result
    {
        return new Result($value);
    }

    public function isSuccess(): bool
    {
        return is_null($this->error);
    }

    public function isError(): bool
    {
        return !$this->isSuccess();
    }

    public static function collect(array $results): Result
    {
        $values = [];
        $errors = [];
        foreach ($results as $result) {
            if ($result->value) {
                $values[] = $result->value;
            }
            if ($result->error) {
                $errors[] = $result->error;
            }
        }
        return new Result($values, $errors);
    }

    public function errorAsString(): string
    {
        if (is_array($this->error)) {
            return implode(', ', $this->error);
        }
        return $this->error;
    }

    public function try($exception_class = null)
    {
        $e = $exception_class ?? null;
        if ($this->isError()) {
            throw new $e($this->errorAsString());
        }
        return $this->value;
    }

    public function map(callable $f): Result
    {
        if ($this->isSuccess()) {
            return static::success($f($this->value));
        }
        return $this;
    }

    public function flatMap(callable $f): Result
    {
        if ($this->isSuccess()) {
            return $f($this->value);
        }
        return $this;
    }
}