遵循协变/逆变原则，避免重复代码的最佳实践

<?php

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'];
}

abstract class BaseBarClass {
    protected $classIndex;
    protected function getFooBase(int $dataIndex) //: ?BaseFooClass  Remove the return type or use : mixed
    {
        // GetRemoteData is assumed to be a global function, the important thing here is the retrieved data depends on classIndex and dataIndex
        // If $classIndex is 1, the $keyValuePairs will look like ['foo1_a' => value1, 'foo1_b' => value2] where value1 and value2 depend on $dataIndex
        $keyValuePairs = GetRemoteData($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
    {
        return $this->getFooBase($dataIndex);
    }
}

class ChildBarClass2 extends BaseBarClass {
    protected $classIndex=2;
    // input to getFoo in each BarClass can be different
    public function getFoo($someInput) : ?ChildFooClass2
    {
        $dataIndex = $this->calculateDataIndex($someInput);
        return $this->getFooBase($dataIndex);
    }
}

// 假设的全局函数
function GetRemoteData(int $classIndex, int $dataIndex): array {
    // 模拟从远程数据源获取数据
    $data = [];
    if ($classIndex == 1) {
        $data = ['foo1_a' => 'value1_' . $dataIndex, 'foo1_b' => 'value2_' . $dataIndex];
    } elseif ($classIndex == 2) {
        $data = ['foo2_a' => 'value3_' . $dataIndex, 'foo2_b' => 'value4_' . $dataIndex, 'foo2_c' => 'value5_' . $dataIndex];
    }
    return $data;
}

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

// 示例用法
$childBar1 = new ChildBarClass1();
$foo1 = $childBar1->getFoo(1);

if ($foo1 instanceof ChildFooClass1) {
    echo "ChildBarClass1::getFoo() 返回了 ChildFooClass1 实例\n";
} else {
    echo "ChildBarClass1::getFoo() 没有返回 ChildFooClass1 实例\n";
}

$childBar2 = new ChildBarClass2();
$foo2 = $childBar2->getFoo('someInput');

if ($foo2 instanceof ChildFooClass2) {
    echo "ChildBarClass2::getFoo() 返回了 ChildFooClass2 实例\n";
} else {
    echo "ChildBarClass2::getFoo() 没有返回 ChildFooClass2 实例\n";
}

?>

abstract class BaseBarClass {
    protected $classIndex;
    protected function getFooBase(int $dataIndex) //: ?BaseFooClass  Remove the return type or use : mixed
    {
        // ...
    }
}