main.cpp

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

#include "RandomChoice.h"

class Base { public: virtual const char* Get() = 0; virtual ~Base() = default; };
class A : public Base { public: const char* Get() { return "A"; } };
class B : public Base { public: const char* Get() { return "B"; } };
class C : public Base { public: const char* Get() { return "C"; } };

int main(int argc, char* argv[])
{
    srand(time(NULL));

    printf("%d\n", RandomChoice(2, 3, 5, 7, 11, 13));
    printf("%s\n", RandomChoice("Bob", "Alice"));
    printf("%d\n", RandomChoice<int (*)()>([] { return 2; }, [] { return 3; } )());

    Base* obj = RandomChoiceNew<Base*, A, B, C>();
    printf("%s\n", obj->Get());
    delete obj;

    return 0;
}

RandomChoice.h

#include <utility>

template <typename T, typename U>
T RandomChoice_Recursive(unsigned choice, unsigned i, U a)
{
    return a;
}

template <typename T, typename U, typename... TArgs>
T RandomChoice_Recursive(unsigned choice, unsigned i, U a, TArgs... tail)
{
    if (i == choice)
        return a;
    else
        return RandomChoice_Recursive<T>(choice, i+1, std::forward<TArgs>(tail)...);
}

template <typename T, typename... TArgs>
T RandomChoice(T a, TArgs... tail)
{
    unsigned num = sizeof...(TArgs) + 1;
    unsigned choice = rand();
    choice %= num;
    return RandomChoice_Recursive<T>(choice, 0, std::forward<T>(a), std::forward<TArgs>(tail)...);
}

template <typename T, typename U, typename... UArgs>
T RandomChoiceNew_Recursive(unsigned choice, unsigned i, UArgs... args)
{
    return new U(args...);
}

template <typename T, typename U, typename V, typename... TArgs, typename... UArgs>
T RandomChoiceNew_Recursive(unsigned choice, unsigned i, UArgs... args)
{
    if (i == choice)
        return new U(args...);
    else
        return RandomChoiceNew_Recursive<T, V, TArgs...>(choice, i+1, std::forward<UArgs>(args)...);
}

template <typename T, typename... TArgs, typename... UArgs>
T RandomChoiceNew(UArgs... args)
{
    unsigned num = sizeof...(TArgs) + 1;
    unsigned choice = rand();
    choice %= num;
    return RandomChoiceNew_Recursive<T, TArgs...>(choice, 0, std::forward<UArgs>(args)...);
}