Not without wasting a lot of space depending on the difference between average size of string vs maximum size of string.

We generally know the maximum string sizes for each property, and they're pretty small, so this wouldn't have been a problem.

You can use a string class like the one in Folly that decays from a fixed array to heap allocated space if the string gets too long.

I believe it's also possible to use variable-size arrays in C or C++ (and end up with a variable-size struct).

Go does allow fixed size arrays in structs, and they're inline in the struct, so `struct { foo [8]uint }` is 32 bytes, whereas `struct { foo []uint }` is 12 bytes and `struct { foo string }` is 8.