Generating cartesian product pairs of any input at compile time
Lambda expressions in combination with parameter packs can be used for complex tasks. In this section, we will implement a function object that accepts an arbitrary number of input parameters and generates the cartesian product of this set with itself.
The cartesian product is a mathematical operation. It is noted as A x B, meaning the cartesian product of set A and set B. The result is another single set, which contains pairs of all item combinations of the sets A and B. The operation basically means, combine every item from A with every item from B. The following diagram illustrates the operation:
In the preceding diagram, if A = (x, y, z), and B = (1, 2, 3), then the cartesian product is (x, 1), (x, 2), (x, 3), (y, 1), (y, 2), and so on.
If we decide that A and B are the same set, say (1, 2), then the cartesian product of that is (1, 1), (1, 2), (2, 1), and (2, 2). In some cases, this might be declared redundant, because the...
