We will get acquainted with tuples, an object that is able to hold a collection of elements, and each element can be of a different type. It is a new feature in C++11 and gives power to functional programming. The tuples will be most useful when creating a function that returns the value. Moreover, since functions don't change the global state in functional programming, we can return the tuples for all the values we need to change instead. Now, let's examine the following piece of code:
/* tuples_1.cpp */
#include <tuple>
#include <iostream>
using namespace std;
auto main() -> int
{
cout << "[tuples_1.cpp]" << endl;
// Initializing two Tuples
tuple<int, string, bool> t1(1, "Robert", true);
auto t2 = make_tuple(2, "Anna", false);
// Displaying t1 Tuple elements
cout << "t1 elements:" << endl;
cout << get<0>(t1) << endl;
cout << get<1>(t1) << endl;
cout << (get<2>(t1) == true ? "Male" : "Female") << endl;
cout << endl;
// Displaying t2 Tuple elements
cout << "t2 elements:" << endl;
cout << get<0>(t2) << endl;
cout << get<1>(t2) << endl;
cout << (get<2>(t2) == true ? "Male" : "Female") << endl;
cout << endl;
return 0;
}In the preceding code, we created two tuples, t1 and t2, with different constructing techniques using tuple<int, string, bool> and make_tuple. However, these two different techniques will give the same result. Obviously, in the code, we access each element in tuples using get<x>(y), where x is the index and y is the tuple object. And, with confidence, we will get the following result on the console:
Another useful member that functions in the tuples classes is tie(), which is used to unpack a tuple into individual objects or create a tuple of lvalue references. Also, we have the ignore helper class in tuples, a placeholder to skip an element when unpacking a tuple is using tie(). Let's see the use of tie() and ignore in the following block of code:
/* tuples_2.cpp */
#include <tuple>
#include <iostream>
using namespace std;
auto main() -> int
{
cout << "[tuples_2.cpp]" << endl;
// Initializing two Tuples
tuple<int, string, bool> t1(1, "Robert", true);
auto t2 = make_tuple(2, "Anna", false);
int i;
string s;
bool b;
// Unpacking t1 Tuples
tie(i, s, b) = t1;
cout << "tie(i, s, b) = t1" << endl;
cout << "i = " << i << endl;
cout << "s = " << s << endl;
cout << "b = " << boolalpha << b << endl;
cout << endl;
// Unpacking t2 Tuples
tie(ignore, s, ignore) = t2;
cout << "tie(ignore, s, ignore) = t2" << endl;
cout << "new i = " << i << endl;
cout << "new s = " << s << endl;
cout << "new b = " << boolalpha << b << endl;
cout << endl;
return 0;
}In the preceding code, we have the same two tuples that tuples_1.cpp has. We want to unpack t1 into variables i, s, and b respectively, using the tie() method. Then, we unpack t2 to the s variable only, ignoring the int and bool data in t2. If we run the code, the output should be as follows:
As we discussed earlier, we can maximize the use of tuples in functional programming when we want to write a function that returns multiple data. Let's take a look at the following block of code to know how to return the tuple and access the return value:
/* tuples_3.cpp */
#include <tuple>
#include <iostream>
using namespace std;
tuple<int, string, bool> GetData(int DataId)
{
if (DataId == 1)
return std::make_tuple(0, "Chloe", false);
else if (DataId == 2)
return std::make_tuple(1, "Bryan", true);
else
return std::make_tuple(2, "Zoey", false);
}
auto main() -> int
{
cout << "[tuples_3.cpp]" << endl;
auto name = GetData(1);
cout << "Details of Id 1" << endl;
cout << "ID = " << get<0>(name) << endl;
cout << "Name = " << get<1>(name) << endl;
cout << "Gender = " << (get<2>(name) == true ?
"Male" : "Female");
cout << endl << endl;
int i;
string s;
bool b;
tie(i, s, b) = GetData(2);
cout << "Details of Id 2" << endl;
cout << "ID = " << i << endl;
cout << "Name = " << s << endl;
cout << "Gender = " << (b == true ? "Male" : "Female");
cout << endl;
return 0;
}As we can see in the preceding code, we have a new function named GetData() returning a Tuple value. From that function, we will consume the data returning from it. We begin with creating the name variable and get the value from the GetData() function. We can also use the tie() method to unpack the tuple coming from the GetData() function, as we can see in the code when we access the data when ID = 2. The output on the console should be like the following screenshot when we run the code:
