boost::有比较价值吗？

发布于 2024-10-11 18:37:04 字数 886 浏览 1 评论 0原文

我有一个 boost::any 向量，想找到这个向量中“any”的索引。

像这样的事情：

vector<any> values;
any valueISearch = ...;
find<A*>(valueISearch);

为此，我尝试使用以下方法比较 2 个任何值：

    template <class T> bool IsValueEqualTo(any aniInVector, any value)
 {
  if (aniInVector.empty() && value.empty())
   return true;

  if (aniInVector.empty() && !value.empty())
   return false;

  if (!aniInVector.empty() && value.empty())
   return false;

  try
  {
   T left = boost::any_cast<T>(aniInVector);
   T right = boost::any_cast<T>(value);

   return left == right;
  }
  catch(const boost::bad_any_cast &exception)
  {
  }

  return false;
 }

问题是，现在当我执行任播时，它只转换为特定类型，而不关心基本类型：

class A {};
class B: public A {};
B v1;
B v2;
IsValueEqualTo<A*>(&v1, &v2);

原文

I have a vector of boost::any and would like to find the index of a 'any' in this vector.

Something like this :

vector<any> values;
any valueISearch = ...;
find<A*>(valueISearch);

For this I try to compare 2 any values with the following method :

    template <class T> bool IsValueEqualTo(any aniInVector, any value)
 {
  if (aniInVector.empty() && value.empty())
   return true;

  if (aniInVector.empty() && !value.empty())
   return false;

  if (!aniInVector.empty() && value.empty())
   return false;

  try
  {
   T left = boost::any_cast<T>(aniInVector);
   T right = boost::any_cast<T>(value);

   return left == right;
  }
  catch(const boost::bad_any_cast &exception)
  {
  }

  return false;
 }

The problem is that now when I do a anycast it only cast to the specific type and don't care about base types :

class A {};
class B: public A {};
B v1;
B v2;
IsValueEqualTo<A*>(&v1, &v2);

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旧城烟雨 2024-10-18 18:37:04

我认为您的问题是 boost::any 库中存在一个基本限制，导致这些类型的转换失败。更一般地说，如果您尝试检索相同类型的对象，则只能使用 any_cast 从 boost::any 恢复对象。例如，这不起作用：

class A { ... };
class B: public A { ... };

boost::any a = new B*;
A* ptr = boost::any_cast<A*>(a); // Cast fails

这是人们一直在抱怨的事情大约有一段时间，但我不知道解决方法。我认为您可能想做的一件事是首先考虑为什么要将 boost::any 与多态性混合在一起。您很有可能绝对必须这样做，但我没有找到在不最大限度地减少 boost::any 的使用的情况下解决此问题的好方法。

I think your problem is that there is a fundamental limitation in the boost::any library that causes these sorts of casts to fail. More generally, you can only recover an object from a boost::any using any_cast if you try to retrieve an object of identical type. For example, this doesn't work:

class A { ... };
class B: public A { ... };

boost::any a = new B*;
A* ptr = boost::any_cast<A*>(a); // Cast fails

This is something that people have been complaining about for a while and I don't know a workaround. I think that one thing you might want to do is consider why you're mixing boost::any with polymorphism in the first place. It's quite possible that you absolutely must do this, but I don't see a good way to fix this without minimizing your use of boost::any.

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