How to make a vector of a type and its name-CodePudding

I have several classes, and I want to make their objects. Each object has different name so as to differentiate with any other object (may be of same type). I want to give the responsibility of making objects to a different function, which takes a vector of {name, class type} elements. Lets say I have 2 structs:

struct A
{
   int i;
}


struct B
{
   int i;
   double d;
}

struct Type
{
    std::string name;    

    template<typename T>
    T t;

    template<typename T>
    using type = decltype(t);
};

std::vector<Type> v{{"ObjA1", A()}, {"ObjB", B()}, {"ObjA2", A()}};

void fun(std::vector<Type> vec)
{
   // use vec to create objects
}

Is this possible to achieve ? Structures A and B are actually classes, provided by some external framework.

CodePudding user response：

I have several classes, and I want to make their objects....

Is this possible to achieve ?

Yes, in c 17 you can. Since you know the types, I would suggest a std::variant<A, B, ...> as a template parameter to the std::vector<Type<...>>.

This required however your struct Type be a class template.

template<typename T> struct Type
{
    std::string name;
    T t;    
    using type = decltype(t);
};

Then we can provide a helper alias type:

#include <variant>

// helper type alias for variats
template<typename... Ts>
using VariantsType = Type<std::variant<Ts...>>;

Now you can write

std::vector<VariantsType<A, B, C>> v{
    {"ObjA1", A{}}, {"ObjB", B{}}, {"ObjA2", A{}}
};
v.emplace_back(VariantsType<A, B, C>{"ObjA3", A{}});
v.emplace_back(VariantsType<A, B, C>{"ObjC1", C{}});
// ... so on

See a demo

CodePudding user response：

If you know what type will be used, you can use variant. If you can not list the types you will use, you can use any. Like

  std::vector<std::any> example;
  example.push_back(1);
  example.push_back("1");
  example.push_back(std::make_pair(1, "1"));