Initializing multiple data structures inside of each other c++11 - c++

Question

I was looking for help on how to initialize the following data structure inside of my constructor for backtracking:
stack<tuple<vector<set<int> >, int, int> > record; //none of the structures have been initialized yet
Thank you all for your help.

Answer 1

When you have a complex type like that, it is helpful to divide the type into fundamental types before figuring out how to initialize it.
Divide your type into fundamental types, it looks like:
stack<tuple<vector<set<int> >, int, int> > record;
^ ^
| |
tuple<vector<set<int> >, int, int>
^ ^ ^ ^ ^ ^
| | | | | |
vector<set<int> >
^ ^
| |
set<int>
^ ^
| |
To initialize an object of such a type, you'll have to figure out how to build up from the constituent fundamental types.
Initialize an int.
int a{0};
Initialize a set<int>.
set<int> b{1, 2};
Initialize a vector<set<int>>.
vector<set<int>> c{ {1, 2}, {2, 3, 4}, {4, 5, 6, 8} };
Initialize a tuple<vector<set<int>>, int, int>.
tuple<vector<set<int>>, int, int> d{ { {1, 2}, {2, 3, 4}, {4, 5, 6, 8} }, 10, 20};
However, you cannot use the same strategy to initialize stack since std::stack does not have a constructor that you can use like:
stack<int> e{1, 3, 5};
That means, you can't initialize a stack<tuple<vector<set<int>>, int, int>> as:
stack<tuple<vector<set<int> >, int, int> > record
{
{{ {1, 2}, {2, 3, 4}, {4, 5, 6, 8} }, 10, 20},
{{ {1, 2}, {2, 3, 4}, {4, 5, 6, 8} }, 10, 20}
};
Your only choice is to default construct record and add items to it.
stack<tuple<vector<set<int> >, int, int> > record;
using item_type = decltype(record)::value_type;
record.push(item_type{{ {1, 2}, {2, 3, 4}, {4, 5, 6, 8} }, 10, 20});
record.push(item_type{{ {1, 2}, {2, 3, 4}, {4, 5, 6, 8} }, 10, 20});