On Mon, 21 Oct 2013 17:34:51 +0100, H. S. Teoh <[email protected]>
wrote:
On Mon, Oct 21, 2013 at 04:41:23PM +0100, Regan Heath wrote:
On Mon, 21 Oct 2013 15:01:04 +0100, H. S. Teoh
<[email protected]> wrote:
>On Mon, Oct 21, 2013 at 11:53:44AM +0100, Regan Heath wrote:
[...]
>>I agree you cannot logically have an existing array that is somehow
>>a "null array" and distinct/different from an empty array, but
>>that's not what I want/am asking for. I want to use an array
>>'reference' to represent that the array is non existent, has not
>>been set, has not been defined, etc. This is what null is for.
>
>The thing is, D slices are value types even though the elements they
>point to are pointed to by reference. If you treat slices (slices
>themselves, that is, not the elements they refer to) as value types,
>then the problem goes away. If you want to have a *reference* to a
>slice, then you simply write T[]* and then it becomes nullable as
>expected.
True, and that's a pointer, and I am comfortable using pointers..
however I worry this will limit the compilers ability to optimise
somehow.. and doesn't it make the code immediately un"safe"?
No, pointers are allowed in @safe. What is not allowed is pointer
*arithmetic* and casting pointers into pointers of different types.
Ah, thanks.
>I do agree that the current situation is confusing, though, mainly
>because you can write `if (arr is null)`, which then makes you think
>of it as a reference type. I think that should be prohibited, and
>slices should be treated as pure value types, and all comparisons
>should be checked with .length (or .empty if you import std.range).
IMO, this would be preferable to the current situation even thought I
would rather go the other way and have a reference type. I can see
the argument that it would be safer and easier for most users, even
though I do not believe I am in that category.
[...]
Well, either way would work, though I do prefer treating slices as value
types. It's just cleaner conceptually, IMO. But I suppose this is one of
those things in which reasonable people may disagree.
I agree that conceptually if you slice something, you cannot get a 'null'
reference. So, a null state for slices makes no sense. However, most
people see arrays as slices, slices as arrays - do you? If so, for arrays
the same conceptual argument does not apply. If not, how do we tell we
have a slice, or an array? If we can't tell, then we have to check for
null with both anyway..
R
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