C++ exam

cpp_exam.md

Problem 7 - Template Meta Programming 2

C++ provides a convenient STL container, tuple. This is an example of using tuple.

auto tuple1 = tuple<int, string, float> (5, "qwe", 0.4f);
auto tuple2 = make_tuple(1, 4, "qqq");

cout<<get<0>(tuple1)<<get<1>(tuple2)<<endl;

Here, get<N, T>(T& t) is a special function template that makes you access to a tuple.

Using a variadic templates, implement a function that couts all elements in any tuple which has only cout-able types.

Q1

First of all, you'll need a special helper class.

template <int...> struct Ints { /* nothing */ }

Implement class templates AtoB, which has typedef mytype = ... that defines Ints instantiated with integers ranged A to B. In other words,

typeid(AtoB<3, 8>::mytype) == typeid(Ints<3,4,5,6,7,8>)

This must hold.

Hints

Use compile-time recursion. Define a base-case specialization.

Q2

Implement the following three function templates.

template <typename T>
void print(tuple<T> a); // base case

template <typename T, typename... Args>
void print(tuple<T, Args...> a); 

template<int ...S, typename... Args>
void temp(Ints<S...> not_used, const tuple<Args...>& t);

Here temp is a helper function that retrieves S... of some instantiated Ints in print. You should call temp from print, and temp should call the recursive N-1 case of print.

print(make_tuple(5, "qwe", 3.0f));
>> 5 qwe 3.0

Hints

Parameter pack expansion can be used being enclosed with another expression. For example,

vector<int> a = {S...}; 
vector<int> b = {abs(S)...}; 
vector<float> c = {sqrt(abs(S))...}; 

Consider using that only in the list initialization and the function arguments passing.