'the data' is a vague concept. Usually, a hash map doesn't expose, for example, the bu met array, or the length of the bucket array. Sure, you can ask the hash map to give you the contents associated with a hash key, but you can't access the entire data structure that the hash map represents.

By contrast, in an 'extreme procedural' style, you would have a struct that is an array of buckets and an integer, and functions that can take such a struct and return information from some particular place inside it. In normal use you would just use the function, but if you're passing your hash map to someone else, there is no longer a guarantee that the length field still matches the actual buckets, or that objects are still arranged into buckets based on their hashes.