Improvements to std.typecons.Nullable

[monarch_dodra]

On Wednesday, 9 October 2013 at 16:34:52 UTC, BLM768 wrote:
> On Wednesday, 9 October 2013 at 06:48:31 UTC, monarch_dodra 
> wrote:
>>
>> OK, so that's two functions already. What about opCmp? What 
>> about toHash?
>
> Since ordered comparisons make no sense with null values, opCmp 
> would need to throw an exception when working with null values 
> anyway. That's exactly what it does right now. I've considered 
> the other operators, and the same logic seems to apply to them.
>
> As for toHash, that needs to be overloaded whenever opEquals 
> is. That's true for all types.
>
>>
>> What if T is a range? Then "Nullable!T.empty" should return 
>> true if the Nullable is empty. IF we don't, we'll get a crash 
>> in foreach.
>
> It does. Null is not an "empty" range; it's the _absence_ of a 
> range. They are not the same concept, and a null range _cannot_ 
> be empty because the range does not exist. Therefore, it's a 
> logic error and should throw an exception.

That was my point. Writting "Nullable!T == T" is the exact same 
thing: Comparison of a value with the absence of a value. It's 
neither equal nor different, it's an error.

>> I draw the line when convenience gets in the way of my 
>> programs not crashing.
>
> Whether you have the "alias this" or not, if you try to get a T 
> out of a null Nullable!T, your program will throw an exception. 
> Leaving out the "alias this" would serve only as a reminder to 
> check for null, not as a solution to logic errors. When dealing 
> with a Nullable!T, just like when dealing with a nullable 
> object reference or a nullable pointer, you have to account for 
> the null state.

My point though is that it's implicit nature makes it so that you 
forget about said state.

Adding a simple ".get()" is not that much verbose, and sticks out 
that you are calling something that can be an error. You should 
either be operating the handler (Nullable), or the Value itself. 
Not a bit of "maybe the nullable, maybe the value"