C++ is most definitely not it.
Lisp is what you are after if you want to include some object system as a library, or a new type of switch statement as a library or a new kind of if statement as a library.
C++ can do none of that.
C++26 reflection alongside compile time code execution, and template metaprogramming, can already do a lot.
It is the best way? Probably not, but we seldom get to chose what mainstream languages win out on the field.
C++ can do some of that. Let's say I want an if statement that takes an integer and three blocks of code. It executes the first block if the integer is less than zero, the second if it is zero, and the third if it is positive.
OK, if you squint enough that by "block of code" you mean closure, or function object, then I can write that in C++. I can make the if statement a free-standing function (that is, not a member of a class), and add it to any library I wish.
Now, you can say that it's going to be tedious to use that, because you have to set up three closures every time you want to call this "super if". And you'd be right, but that's a different argument.