I think you’re confusing zero cost with zero overhead.

What C++ programmers like is that the compiler does not add overhead, for example calling `a[10]` will read the word at address `a + 10` and return that. No bounds checks are inserted, no function call is done to lookup the element in some implementation defined sparse data structure, etc.

But C++ programmers are generally not opposed to using things that has a cost associated with it (basically everything has a cost) — for example `std::map` is quite popular and certainly not “zero cost”, though it has its running time defined, and the implementation is actually using a self-balancing search tree rather than a hash table because we can give guarantees about the running time of the former, not the latter.