array of elements of various sybtypes

[Steven Schveighoffer]

On Wed, 26 Jan 2011 12:30:17 -0500, spir <denis.spir at gmail.com> wrote:

> On 01/26/2011 06:27 PM, spir wrote:
>> Hello,
>>
>> This fails:
>>
>> class T0 {}
>> class T1 : T0 {}
>> class T2 : T0 {}
>>
>> unittest {
>> auto t1 = new T1();
>> auto t2 = new T2();
>> T0[] ts = [t1, t2];
>> }
>>
>> Error: cannot implicitly convert expression (t1) of type __trials__.T0  
>> to
>> __trials__.T2
>> Error: cannot implicitly convert expression ([(__error),t2]) of type  
>> T2[] to T0[]
>>
>> I guess it should be accepted due to explicite typing 'T0[]'. What do  
>> you
>> think? D first determines the type of the last element (always the last  
>> one),
>> here T2. Then, /ignoring/ the array's defined type, tries to cast other
>> elements to the same type T2. It should instead, I guess, check all  
>> elements
>> are compatible with the defined array type.
>> An additional enigma is why the failing element t1 is said to be of  
>> supertype
>> T0 --which is also correct-- while it retained t2's exact type T2. ???
>>
>> Anyway, is there a workaround?
>
> PS: this works, but I would prefere a solution with all casting:
>      T0[] ts = [cast(T0)t1, cast(T0)t2];
> I consider this issue a bug, at least when the array is explicitely  
> typed. What do you think?

It's not a bug, the type of an expression does not depend on the type it's  
assigned to.  Essentially [t1, t2] is evaluated *before* looking at what  
it's assigned to.

And the array literal code now uses the most 'compatible' type to  
determine the type of the array (used to be hard-typed to type of first  
element).  Obviously it doesn't work correctly here, but I'm not sure it  
could really work correctly.  I think maybe if one of those elements had  
type T0, it might actually compile.

-Steve