可选的函数参数：使用默认参数（NULL）或重载函数？ [英] Optional function parameters: Use default arguments (NULL) or overload the function?

问题描述

我有一个函数处理给定的向量，但也可以创建这样的向量本身，如果没有给出。

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，我看到两个设计选择，其中一个函数参数是可选的：

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

指针，并使它 NULL 默认情况下：

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
}

或者有两个函数有一个重载的名字，其中一个没有参数：

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
}

有理由更喜欢一种解决方案吗？

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a const ，只读，不写。此外，界面看起来更干净（不是 NULL 只是一个黑客？）。而且间接函数调用产生的性能差异可能被优化掉了。

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，我经常看到代码中的第一个解决方案。有没有令人信服的理由喜欢它，除了程序员的懒惰？

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

推荐答案

我肯定会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，因为它不再具有单一明确定义的目的。这反过来增加了代码的复杂性，使得不熟悉它的人更难以理解它。

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.

第二种方法（重载方法），每个方法都有一个明确的目的。每种方法都是结构良好的和 cohesive 。一些其他注意事项：

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

• 如果有需要复制到两种方法的代码，可以将它们提取到单独的方法，每个重载的方法都可以调用这个外部方法。


• 我会进一步和 。这将使代码更自我记录。

• 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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