Criticizing Hare language approach for generic data structures

We have discussed adding first-class maps to the language many times. We recognize the value in this feature and have tried to come up with a good way of doing it that fits within the design constraints of the language, but it has several design issues. There are three key problems: finding a good way of hashing arbitrary data structures (or arbitrarily limiting the kinds of keys the map can store), finding a good way of determining equality of arbitrary data structures, and dealing with memory allocation semantics. Hare does not have generics, and the alternative is a hands-free approach to hashing and equality, which has some troubling limitations, some of which are very unintuitive and non-obvious (which conflicts with our values for explicitness). The allocation problem is also troublesome: Hare uses manual memory management, and any hash map solution which involves magic behind-the-scenes allocations has serious design conflicts with Hare's principles.

This article criticizes a sample of a hash map implemented for the build driver. This hash map is used to store a mapping of module details keyed on the module's namespace. It is true that it is a fixed size map, and that collisions can easily be found for the fnv32 hash. These constraints limit the ability for this hash map design to generalize. However, this is not supposed to generalize. It's designed to be a special-purpose hash map for this specific use-case, and takes the simplest approach which is sufficient to this specific problem. As the author notes, there are many approaches to hash maps and there is no one-size-fits-all solution. So far as hash collisions are concerned, these are very unlikely in this use-case. This is not a hash map where hash flooding is a concern, and accidental collisions are so unlikely as to be a negligible risk. If this were not the case, it is easily fixed by just comparing each bucket entry by the namespace rather than by the hash. For use-cases where these things do matter, I would be interested in seeing something like siphash end up in the Hare standard library.

Recall that Hare is designed to be similar to C in terms of scope and goals. C also provides no general-purpose hash map, and little by way of other data structures (though some attempts exist, none of them good). Each of these approaches and concerns comes with different needs and trade-offs, and Hare places responsibility for evaluating these needs and trade-offs into the capable hands of the programmer. This is a reflection of Hare's values, which are distinct from the values of some other languages mentioned in the OP - Rust, Go, Zig, C++, etc.

Thanks for providing me the opportunity to clarify this here, though perhaps this merited a blog post rather than an overlong HN comment. I understand that this is a design decision which appears especially confusing from the outside, but know that it was made through careful deliberation and discussion.

Oh-- and a map-like thing for net::uri would be nice to have as a convenience function in the future. We need to implement the basic approach using the most fundamental design and then build the convenience on top of it, in order to accommodate all use-cases and leave the trade-offs for the user to make.

So if I need a hash table to map inodes to strings and another to map strings to IP addresses, I'll need to create that anew each time.

That means either writing a lot of code twice, or relying on manual code generation (which sucks for many reasons).

C is a terrible language for building things in the modern world. Not including the progress over the last 4 decades in your new language is a mistake.

The entire issue is that the language does not allow for that: like Go (pre 1.18) it does not have userland generics. And unlike Go it doesn't even have a builtin hashmap, only arrays and slices.