store string data in a struct along with length

[ngoldbaum]

This makes the dtype store the string data in a struct:

typedef struct ss {
    size_t len;
    char buf[];
} ss;

So far this is just a refactoring but the hope is that storing the length will avoid O(N) strlen calls and make it easier to write code that doesn't accidentally introduce buffer overflows.

Bikeshedding on the naming and the API are very welcome.

[seberg]

Storing the length explicitly also means you can represent strings like "a\0" correctly (NumPy strings cannot).

I don't feel like bike-shedding storage. There are probably many options. If there is a chance of wanting to play with schemes that store length in the array itself then using accessor static inline functions or macros might make sense for getting length and chars/buf.

In theory int is enough for length storage for the forseeable future, but I guess it doesn't matter.

[peytondmurray]

Can you short-circuit the strncmp if the ss lengths are different?

[peytondmurray]

Optional small change 🚀 thanks for this!