有没有一些忍者的技巧，使其变量常量后声明？ [英] Is there some ninja trick to make a variable constant after its declaration?

问题描述

我知道答案是99.99％没有，但我认为这是值得一试，你永远不知道。

  SomeFunction（int a）
 {
 //这里有一些处理，例如：
a * = 50; 
 a％= 10; 
 if（example（））
 a = 0; 
 //从这一点上我想使aconst;我不想允许
 //任何超过这个注释的代码以任何方式修改它。 
} 
  

我可以做一些类似于 const int b = a; ，但它不是真的相同，它造成了很多困惑。

编辑：另一个抽象不太好的例子，一个让我问这个问题：

/ p>

  void OpenFile（string path）
 {
 boost :: to_lower（path）; 
 //我想让路径成为常数
 ifstream ... 
} 
  

EDIT ：另一个具体示例：在并行部分中的变量上重新捕获常量 。

解决方案

一个解决方案是将所有的突变代码放入lambda表达式。执行lambda表达式中的所有变异，并将结果分配给方法范围中的 const int 。例如

  void SomeFunction（const int p1）{
 auto calcA = [& $ b int a = p1; 
 a * = 50; 
 a％= 10; 
 if（example（））
 a = 0; 
 .. 
 return a; 
}; 
 const int a = calcA（）; 
 ... 
} 
  

I know the answer is 99.99% no, but I figured it was worth a try, you never know.

void SomeFunction(int a)
{
    // Here some processing happens on a, for example:
    a *= 50;
    a %= 10;
    if(example())
       a = 0;
    // From this point on I want to make "a" const; I don't want to allow
    // any code past this comment to modify it in any way.
}

I can do something somewhat similar with const int b = a;, but it's not really the same and it creates a lot of confusion. A C++0x-only solution is acceptable.

EDIT: another less abstracted example, the one that made me ask this question:

void OpenFile(string path)
{
    boost::to_lower(path);
    // I want path to be constant now
    ifstream ...
}

EDIT: another concrete example: Recapture const-ness on variables in a parallel section.

解决方案

One solution would be to factor all of the mutation code into a lambda expression. Do all of the mutation in the lambda expression and assign the result out to a const int in the method scope. For example

void SomeFunction(const int p1) { 
  auto calcA = [&]() {
    int a = p1;
    a *= 50;
    a %= 10;
    if(example())
       a = 0;
    ..
    return a;
  };
  const int a = calcA();
  ...
}

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