PHP中协变与逆变规则下的代码复用与类型安全实践

class BaseFooClass {
    protected $keys = [];
    private $map = [];
    public function __construct($keyValuePairs) {
        foreach($this->keys as $key => $value) {
            $this->map[$key] = $keyValuePairs[$key] ?? null;
        }
    }
}

class ChildFooClass1 extends BaseFooClass {
    protected $keys = ['foo1_a', 'foo1_b'];
}

class ChildFooClass2 extends BaseFooClass {
    protected $keys = ['foo2_a', 'foo2_b', 'foo2_c'];
}

// ... 大量 ChildFooClass 子类

abstract class BaseBarClass {
    protected $classIndex;
    protected function getFooBase(int $dataIndex) : ?BaseFooClass 
    {
        // 假设 GetRemoteData 和 checkDataIntegrity 是全局函数
        $keyValuePairs = GetRemoteData($this->classIndex, $dataIndex);
        if (checkDataIntegrity($keyValuePairs)) {
            $class = "ChildFooClass" . $this->classIndex;
            return new $class($keyValuePairs);
        }
        return null;
    }
}

class ChildBarClass1 extends BaseBarClass {
    protected $classIndex=1;
    public function getFoo(int $dataIndex) : ?ChildFooClass1 
    {
        // 这里违反了协变规则：getFooBase返回BaseFooClass，但getFoo期望ChildFooClass1
        return $this->getFooBase($dataIndex);
    }
}

class ChildBarClass2 extends BaseBarClass {
    protected $classIndex=2;
    public function getFoo($someInput) : ?ChildFooClass2
    {
        $dataIndex = $this->calculateDataIndex($someInput);
        // 同样违反了协变规则
        return $this->getFooBase($dataIndex);
    }
}

class BaseFooClass {
    protected $keys = [];
    private $map = [];
    public function __construct($keyValuePairs) {
        foreach($this->keys as $key => $value) {
            $this->map[$key] = $keyValuePairs[$key] ?? null;
        }
    }
}

class ChildFooClass1 extends BaseFooClass {
    protected $keys = ['foo1_a', 'foo1_b'];
}

class ChildFooClass2 extends BaseFooClass {
    protected $keys = ['foo2_a', 'foo2_b', 'foo2_c'];
}

// ... 大量 ChildFooClass 子类

abstract class BaseBarClass {
    protected $classIndex;

    // 移除返回类型声明 (PHP 7.x)
    // 或者使用 : mixed (PHP 8+)
    protected function getFooBase(int $dataIndex) /* : mixed (PHP 8+) */
    {
        $keyValuePairs = GetRemoteData($this->classIndex, $dataIndex);
        if (checkDataIntegrity($keyValuePairs)) {
            $class = "ChildFooClass" . $this->classIndex;
            return new $class($keyValuePairs);
        }
        return null;
    }
}

class ChildBarClass1 extends BaseBarClass {
    protected $classIndex=1;
    public function getFoo(int $dataIndex) : ?ChildFooClass1 
    {
        // 现在不再违反协变规则
        return $this->getFooBase($dataIndex);
    }
}

class ChildBarClass2 extends BaseBarClass {
    protected $classIndex=2;
    public function getFoo($someInput) : ?ChildFooClass2
    {
        $dataIndex = $this->calculateDataIndex($someInput);
        // 同样不再违反协变规则
        return $this->getFooBase($dataIndex);
    }

    // 假设的辅助方法
    private function calculateDataIndex($someInput): int {
        // 实际计算逻辑
        return (int)$someInput;
    }
}

// 假设的全局函数
function GetRemoteData(int $classIndex, int $dataIndex): array {
    // 模拟从远程获取数据
    if ($classIndex === 1) {
        return ['foo1_a' => "value1_a_{$dataIndex}", 'foo1_b' => "value1_b_{$dataIndex}"];
    } elseif ($classIndex === 2) {
        return ['foo2_a' => "value2_a_{$dataIndex}", 'foo2_b' => "value2_b_{$dataIndex}", 'foo2_c' => "value2_c_{$dataIndex}"];
    }
    return [];
}

function checkDataIntegrity(array $data): bool {
    // 模拟数据完整性检查
    return !empty($data);
}

// 示例使用
$bar1 = new ChildBarClass1();
$foo1 = $bar1->getFoo(10);
if ($foo1 instanceof ChildFooClass1) {
    echo "ChildFooClass1 instance created successfully.\n";
}

$bar2 = new ChildBarClass2();
$foo2 = $bar2->getFoo(20);
if ($foo2 instanceof ChildFooClass2) {
    echo "ChildFooClass2 instance created successfully.\n";
}