c++ - 根据参数在构造函数中设置成员数据类型

Question

我有一个以枚举值作为参数的类。它有一个成员 m_ConsistencyErrors 这是 std::set .我想根据枚举参数的值在构造时设置此成员的类型。

if TestType value is MSG123_CONSISTENCY_TEST I would like m_ConsistencyErrors to be of type std::set<EnMsg123Param>

if TestType value is MSG5_CONSISTENCY_TEST I would like m_ConsistencyErrors to be of type std::set<EnMsg5Param>

是否有一种干净的方法来实现这一点，或者我应该找到另一种解决方案。

class CMsgConsistencyTest // : public CTestBase  // left out for simplicity
{
    enum EnTests
    {
        MSG123_CONSISTENCY_TEST,
        MSG5_CONSISTENCY_TEST,
    };
    enum EnMsg123Param
    {
        Msg123_1,
        Msg123_2
    };
    enum EnMsg5Param
    {
        Msg5_1,
        Msg5_2
    };

public:
    CMsgConsistencyTest(const EnTests TestType) //  : CTestBase(TestType)  // left out for simplicity
    {
        if (TestType == MSG123_CONSISTENCY_TEST)
        {
            ParameterType = EnMsg123Param;  // pseudo code
        }
        else if (TestType == MSG5_CONSISTENCY_TEST)
        {
            ParameterType = EnMsg5Param;  // pseudo code
        }
    }

private:
    template<typename ParameterType>
    std::set<ParameterType> m_ConsistencyErrors;
};

Answer 1

你不能那样做，当你使用 CMsgConsistencyTest 并且当它的成员访问 m_ConsistencyErrors

时， ParameterType 必须一直知道>

CMsgConsistencyTest 可以是模板类，例如

#include <set>

enum EnMsg123Param
{
  Msg123_1,
  Msg123_2,
};

enum EnMsg5Param
{
  Msg5_1,
  Msg5_2,
  Msg5_3,
};

template<typename ParameterType>
class CMsgConsistencyTest // : public CTestBase  // left out for simplicity
{
  public:
    // ...
  private:
    std::set<ParameterType> m_ConsistencyErrors;
};

// and for instance

CMsgConsistencyTest<EnMsg123Param> A;
CMsgConsistencyTest<EnMsg5Param> B;

否则你可能不得不做一些丑陋的、灾难性的和“非 C++”的事情:

   CMsgConsistencyTest(const EnTests TestType) //  : CTestBase(TestType)  // left out for simplicity
    {
        if (TestType == MSG123_CONSISTENCY_TEST)
        {
            m_ConsistencyErrors = new set<EnMsg123Param>;
        }
        else if (TestType == MSG5_CONSISTENCY_TEST)
        {
            m_ConsistencyErrors = new set<EnMsg5Param>;
        }
        // else ?
        // probably need to save TestType etc
    }

private:
    void * m_ConsistencyErrors;