The demise of T[new]

[Andrei Alexandrescu]

Leandro Lucarella wrote:
> Andrei Alexandrescu, el 19 de octubre a las 11:16 me escribiste:
>>>>> I'm missing something? Why this shouldn't work?
>>>> It may work, but I was unable to pull it off reasonably well.
>>> What problems did you find?
>> I thought I explained that above and in several other posts. I have
>> the feeling this is going in circles, but let me add one more thing.
>> People would want to have a reasonable way of choosing between
>> T[new] and T[]. The differences between them are subtle (I have two
>> tables showing the primitives of T[] and T[new], which are very
>> similar).
> 
> If T[new] is "array" and T[] is "slice" as I described them, I see no
> subtlety, they are huge differences, one is a dynamic array, the other is
> a view on somebody else's memory.

Their primitives overlap 90% in syntax and semantics.

> I know you probably hate when people says this (that's what I avoided
> doing it before :):
> I works very well in Python. You have arrays (well, lists, but the
> interface is the same as an array) and slices. I never heard anybody
> complaining about that being confusing.

Python lists and slices are quite different from D arrays.

>> That static decision concerns future appends to the array,
>> which doesn't strike me as something you know from the get-go
>> through future iterations of a design. Use of "auto" messes up
>> things further: a nice function may choose to return T[new] because
>> it just created an array (an implementation detail), but clients may
>> find that unexpected.
> 
> I don't see much problem. You should always return an array (T[new]) if
> you have one, because you can get an slice from it (the inverse is not
> true). Because of this, implicit conversion from array to slice can be
> a good idea, so people expecting a slice when an array is returned will
> never know an array was returned anyways. If you need to keep appending to
> the array, you can have the original array and keep appending to it
> without any performance hit (no copying, no new allocations).
> 
> What's wrong with that?

People expecting a slice and using "auto" or templates are in for a rude 
awakening.


Andrei