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Comment by electrograv | Hacker News Reader

The downside to using a non-inlined conversion function is that (1) it will be slower than just accessing the member directly, and (2) it’s much more verbose.

Why not just use the member explicitly? This way, converting a STS string into a legacy C string could be as simple as writing “.cstr” (or if you just be as terse as possible, it could be defined as “.s” as another poster suggests).

In this case, compromise of increased code verbosity is extremely minor at worst (just a few characters). At best, this extra explicitness can actually be seen as a good thing for code readability (not to mention the huge benefits we’re discussing of type safety).

So the question then is: Why doesn’t SDS do this? The actual library uses a regular C typedef (which is unsafe for the reasons described above).

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I think you're missing the point here, the conversion function is trivially inlinable:

    char* sds_cstr(sds *str){
        return &str[0]; //you could probably just cast too
    }

The other posters solution is actually not equivalent in this way (his sds is convertable to char* instead of sds*).

Even an inlined function only has value if our goal is to open the door to implementation changes in the future. But because the current implementation is zero-cost (an inlined no-op), any behavioral change will necessary compromise performance.

Otherwise (if we want to retain the zero-cost guarantee of converting to a C string), directly accessing the member variable is: functionally equivalent, simpler, more concise, more readable, more explicit.

I actually prefer the inline function here (while making the member char* private when compiling as C++), since that mostly prevents assignment to the member variable in settings where that would not be a valid operation.

With that said, I agree that the additional verbosity is a significant drawback, and I can understand going with the slightly-less-safe option for that reason alone.

Ah, that’s a good point. I’m a fan of extra safety, though we’d need to make a few extra changes to get around C’s lack of private variables: We could make the internal member instead a size_t, and cast to pointer form when needed inside the library or when converting via this inline function (which is still a no-op in terms of performance). The only major downside then remaining is perhaps syntax/verbosity, which IMO is secondary to safety.

However: If we open the discussion up to C++, then this is pretty easy to solve without any real syntactic or performance compromise: we can make a class/struct which defines implicit conversions to C strings, and disables any implicit conversions from C strings.

Good point about implicit conversions; I may actually be able to use that to clean up some code in the near future.

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