D2 toStringz Return Type

[Steven Schveighoffer]

"Andrei Alexandrescu" wrote
> Steven Schveighoffer wrote:
>> "Andrei Alexandrescu" wrote
>>> Steven Schveighoffer wrote:
>>>> "Andrei Alexandrescu" wrote
>>>>> Mike Parker wrote:
>>>>>> I'm curious as to why toStringz in D2 returns const(char)* instead of 
>>>>>> just a plain char*. Considering that the primary use case foe the 
>>>>>> function is interfacing with C code, it seems rather pointless to 
>>>>>> return a const(char)*.
>>>>> We want to leave the opportunity open to not duplicate the actual 
>>>>> memory underneath the string object. (Right now that opportunity is 
>>>>> not effected.)
>>>> My recommendation -- have 2 functions.  One which always copies (and 
>>>> returns char *), and one which does not.
>>>>
>>>> This at least leaves a safe alternative for people who have headers 
>>>> that aren't properly constified, and don't want to go through the 
>>>> hassle of looking it up themselves.  Also good for those C functions 
>>>> which actually require a mutable char *, since D2 strings are mostly 
>>>> invariant.
>>> You can't quite do that because dynamic conditions establish whether 
>>> it's safe to avoid copying or not.
>>
>> I can see how you interpreted it this way.
>>
>> What I meant was one is the toStringz as it is today, which might copy 
>> and might leave it in-place.  This can be used to call C functions that 
>> take a const char *.  The other function will *always* copy, and will 
>> return a mutable char *.  This is for when you don't care to look at the 
>> function yourself (assuming the author got it correct), or the case where 
>> the C function actually does mutate the argument.
>>
>> If the C function does actually require a mutable argument, you are 
>> forced to do an extra dup for no reason with today's toStringz.
>>
>> -Steve
>
> I see. So:
>
> const(char)* toStringzMayOrMayNotCopy(in char[]);
> char* toStringzWillAlwaysCopy(in char[]);
>
> Providing writable zero-terminated strings is a sure recipe for disaster
>  (see the debates around sprintf, strcpy etc.). I think the need for
> such things is rare and at best avoided entirely by the standard
> library. If you so wish, you can always use malloc by hand.

Using zero terminated strings, even const ones, is a recipe for disaster. 
Yet, there it is.  And it's making me do 2 duplications.

The reality is that as soon as you cross the boundary from D to C, you have 
lost all the safety benefits that D provides, even if the signature is 
const.  The reality is, people are still going to call these functions, 
either with an extra dup (which buys you nothing in safety), or by editing 
the bindings to be const (which makes it even more unsafe).  The reality is, 
most of these calls are pretty innocuous.  People aren't using sprintf or 
strcpy, they are using C libraries that do things that D doesn't already do. 
Most of these are just using char * as a way to pass const strings, it isn't 
too much to ask for a function that complies.

But you probably won't add it.  That's ok, I don't use Phobos anyways.  I'll 
be sure to add an appropriate function to Tango while porting it to D2.

-Steve