On 01/26/2011 07:26 PM, Steven Schveighoffer wrote:
On Wed, 26 Jan 2011 12:30:17 -0500, spir <denis.s...@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.
The said element should be, I guess, the last one (seems D start evaluating
elements from the right?).
EDIT: this works:
auto t0 = new T0();
auto t1 = new T1();
auto t2 = new T2();
T0[] ts = [t0, t1, t2];
Seems D check compatibility between actual element types. In the original case
of [t1, t2], it does not "see" that T1 & T2 have a common supertype.
I would like to know why the original error message assigns speaks of type T0
(for t1, obviously).
What about a workaround? Hum... This works:
void feed (T) (ref T[] array, T[] elements...) {
foreach (element ; elements)
array ~= element;
}
unittest {
auto t1 = new T1();
auto t2 = new T2();
T0[] array;
array.feed(t1, t2);
writeln(array);
}
The trick indeed is using '...'. May feed be useful in std.array? (With a
variant for AAs?)
(Called it feed instead of init because it can also extend a non-empty array,
with a set of new elements one could not write literally, neither.)
Denis
--
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vita es estrany
spir.wikidot.com
