可选函数参数:使用默认参数 (NULL) 还是重载函数?

2021-12-29 00:00:00 function null overloading parameters c++

我有一个函数可以处理给定的向量，但如果没有给出，也可以自己创建这样的向量.

I have a function that processes a given vector, but may also create such a vector itself if it is not given.

对于这种情况，我看到了两种设计选择，其中函数参数是可选的:

I see two design choices for such a case, where a function parameter is optional:

使其成为一个指针并使其默认为NULL:

Make it a pointer and make it NULL by default:

void foo(int i, std::vector<int>* optional = NULL) {
  if(optional == NULL){
    optional = new std::vector<int>();
    // fill vector with data
  }
  // process vector
}

或者有两个具有重载名称的函数，其中一个省略了参数:

Or have two functions with an overloaded name, one of which leaves out the argument:

void foo(int i) {
   std::vector<int> vec;
   // fill vec with data
   foo(i, vec);
}

void foo(int i, const std::vector<int>& optional) {
  // process vector
}

是否有理由更喜欢一种解决方案?

Are there reasons to prefer one solution over the other?

我稍微喜欢第二个，因为我可以使向量成为 const 引用，因为它在提供时只能读取，不能写入.此外，界面看起来更干净(是不是 NULL 只是一个黑客?).并且可能会优化掉间接函数调用导致的性能差异.

I slightly prefer the second one because I can make the vector a const reference, since it is, when provided, only read, not written. Also, the interface looks cleaner (isn't NULL just a hack?). And the performance difference resulting from the indirect function call is probably optimized away.

然而，我经常在代码中看到第一个解决方案.除了程序员的懒惰之外，是否有令人信服的理由更喜欢它?

Yet, I often see the first solution in code. Are there compelling reasons to prefer it, apart from programmer laziness?

推荐答案

我绝对喜欢重载方法的第二种方法.

I would definitely favour the 2nd approach of overloaded methods.

第一种方法(可选参数)模糊了方法的定义，因为它不再有一个明确定义的目的.这反过来又增加了代码的复杂性，让不熟悉它的人更难理解它.

The first approach (optional parameters) blurs the definition of the method as it no longer has a single well-defined purpose. This in turn increases the complexity of the code, making it more difficult for someone not familiar with it to understand it.

对于第二种方法(重载方法)，每种方法都有明确的目的.每种方法都是结构良好和内聚.一些附加说明:

With the second approach (overloaded methods), each method has a clear purpose. Each method is well-structured and cohesive. Some additional notes:

  • 如果有代码需要复制到两个方法中，可以提取到一个单独的方法中，每个重载的方法都可以调用这个外部方法.
  • 我会更进一步，为每个方法命名不同以表明方法之间的差异.这将使代码更具自文档性.
  • If there's code which needs to be duplicated into both methods, this can be extracted out into a separate method and each overloaded method could call this external method.
  • I would go a step further and name each method differently to indicate the differences between the methods. This will make the code more self-documenting.

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