CODEWITHSUNDEEP
c++boost
Michael
Michael

Reputation: 712

How to use boost is_class to determine if an object is a class?

For below code:

template<class _InIt,
class _Ty,
class _Fn2> inline
_Ty accumulateSimplePtr(_InIt _First, _InIt _Last, _Ty _Val, _Fn2 _Func)
{   // return sum of _Val and all in [_First, _Last), using _Func
for (; _First != _Last; ++_First)
{
    if(is_class<std::iterator_traits<_InIt>::value_type>::value)
        _Val = _Func(_Val, (*_First)());
    else
        _Val=_Func(_Val, *_First);
}
            return (_Val);
}

how can i tell if _InIt is an interator that is pointing to a class/struct or to a pod such as double?

If it is pointing to a double, I want to use *_First to get the data, and if it points to a class, I would use (*_First)() to get the actual data(assuming that the class has an overloaded operator().

I tried something as above, but it failed to compile with line " _Val=_Func(_Val, *_First);", saying that MyObj can't be convereted to double.

Upvotes: 0

Views: 416

Answers (1)

Borgleader
Borgleader

Reputation: 15916

#include <iostream>
#include <type_traits>
#include <vector>

class A
{
public:
    int a;
    int b;
};

template<typename T>
struct IsClass
{
    enum { Yes = std::is_class<T>::value };
    enum { No = !Yes };
};

int main(int argc, char* argv[])
{
    std::vector<int> v1;
    std::vector<A> v2;
    auto it1 = v1.begin();
    auto it2 = v2.begin();

    std::cout << IsClass<std::decay<decltype(it1)>::type::value_type>::Yes << std::endl;
    std::cout << IsClass<std::decay<decltype(it2)>::type::value_type>::Yes << std::endl;

    std::cin.get();
    return 0;
}

The output for these the lines is 0 (false, for int vector) and 1 (true, for A vector).

Upvotes: 1

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