If i understand correctly:
std::span<char> v("123", 3)
hash_append(h, v); // hash "123" + the size 3, as v is a container h.update(v); // hash only "123".
Or did i miss something?
I think this is actually an important question: How to (conveniently) hash only a range? I.e. with the library, not the hasher. As in the example there might be use cases to calculate e.g. the checksum of a file using the hash algorithm as a template. For this the size of the data/file must not be included in the hash. I've seen `hash_append_range` which could be used but needs to get the begin/end manually. I think a 3 parameter form `hash_append_range(Hash&, Flavor&, Range)` would be a good addition to support the above use case without having to call the hasher directly. I.e. to provide a similar interface/abstraction to `hash_append` Maybe name it `hash_append_range_without_size` to discourage people from using it without knowing the caveats (multiple ranges, empty ranges, ...)