Dynamically sized heterogenous collections
We started this chapter by noting that the dynamically sized containers offered by C++ are homogenous, meaning that we can only store elements of one single type. But sometimes, we need to keep track of a collection that's dynamic in size that contains elements of different types. To be able to do that, we will use containers that contain elements of type std::any or std::variant.
The simplest solution is to use std::any as the base type. The std::any object can store any type of value in it:
auto container = std::vector<std::any>{42, "hi", true};
It has some drawbacks, though. First, every time a value in it is accessed, the type must be tested for at runtime. In other words, we completely lose the type information of the stored value at compile time. Rather, we have to rely on runtime type checks for the information. Secondly, it allocates the object on the heap rather than the stack, which can have significant...
