alt Hacker News> This is still compatible with a C string
Strictly speaking, it's not alignment compatible from CString to BSTR unless you declare all strings to be at most 255 characters or the cpu architecture doesn't require aligned access for multi-byte words (like x86). The BSTR alignment must match the alignment of the length word, meaning you can't convert a randomly-aligned C string to BSTR by simply attaching a prefix in-place.
Also, having the length embedded in the value rather than in the pointer makes it impossible to create BSTR (sub)slices without performing a memcpy. Fat pointers do not have this restriction.
A BSTR object is compatible with functions expecting a C string. The other direction obviously never holds, unless the C string is a BSTR to start with.
Yes, there is a trade-off between slices using the same format and having compatibility with C strings. Hence “middle ground”.
You can still use a string-slice type on top of BSTR, it just would be a separate additional type. Note that languages like Java also don’t have a singular type for strings and string slices.