std.path review: update

[Andrei Alexandrescu]

On 7/18/11 7:23 AM, torhu wrote:
> On 18.07.2011 11:42, Lars T. Kyllingstad wrote:
>> On Sun, 17 Jul 2011 22:38:43 -0700, Jonathan M Davis wrote:
>>
>>> On Sunday 17 July 2011 22:08:27 Brian Schott wrote:
>>>> The documentation comments for driveName say that the return value will
>>>> be an empty string in some circumstances, but the code and unit tests
>>>> both say that the behavior is to return null.
>>>
>>> The fun part with that is that "" == null and a null string is empty per
>>> std.array.empty, so it _is_ the empty string. The only difference is
>>> that "" !is null. So, if the function says that it returns null, then it
>>> needs to return null. Since it says that it returns the empty string, it
>>> could return either.
>>>
>>> Now, in spite of all that, there's still a problem since the tests
>>> verify that the return value is null, not empty. Either the
>>> documentation should say that it returns null, or the tests should be
>>> checking for empty, not null. But still, the documentation isn't
>>> incorrect. Are the tests are perfectly valid, but they really shouldn't
>>> be testing for is null instead of empty when the function is supposed to
>>> return empty.
>>
>> Pending a decision on the null vs. empty issue, I have now standardised
>> on using empty() for testing whether functions return empty strings.
>
> I'd like to make a case for null as the 'nothing here' value.
>
> The advantage of using null is that all possible ways of testing for
> 'nothingness' (is, ==, as a boolean condition, empty range) will work.
> But if you return an empty string, you can't do 'str is null', because
> that will be false. With null there's just no doubt, and no way to get
> the test wrong.

Note that there are two aspects: generating 'nothing here' values, and 
testing for 'nothing here'.

In keeping with the "be generous with what you receive and conservative 
with what you send" mantra, good functions should test string inputs 
with str.empty and return null strings.


Andrei