On Mon, 16 May 2011 16:12:05 -0400, nrgyzer <nrgy...@gmail.com> wrote:
== Auszug aus Steven Schveighoffer (schvei...@yahoo.com)'s Artikel
On Mon, 16 May 2011 15:32:43 -0400, useo <unkn...@unknown.com>
wrote:
> Hey guys,
>
> is there any chance to create an abstract constructor like:
>
> abstract class ABC {
>
> abstract this();
>
> }
>
> DMD always says "...this non-virtual functions cannot be
abstract" -
> when I use an interface like:
>
> interface ABC {
>
> this();
>
> }
>
> I get a similar error: "...constructors, destructors, postblits,
> invariants, unittests, new and delete functions are not allowed in
> interface ABC"
>
> Is there any solution or is it possible to create such
inheritances
> in DMD?
I think what you are trying to do is say, "if a class implements
interface
ABC, it must have a default constructor". Such a requirement is
faulty.
The point of an interface is to able to pass a portion of a class'
functionality to a function during runtime. However, the instance
must
*already exist*. It makes no sense to posit requirements on the
constructor.
What you want is a compile-time requirement using a template
constraint.
You may think "damn, but I don't want to make my function a
template", I'd
say see previous point ;)
-Steve
Okay, thanks... perhaps someone know a better solution: I have one
big file which contains some other files (let's say: blocks). Each
block has it's own signature... by reading the big file, I read the
signature of each block. Based on the signature, I read block A,
block B or another Block. To do that, I want call the block-specific
constructor which reads the next bytes.
!Semicode:
...
ABC[] blocks;
...
while (!eof(bigfile)) {
read(signature);
if (signature==A) blocks ~= new A(bigfile);
else if (signature==B) blocks ~= new B(bigfile);
...
}
...
No special requirements are necessary. How would this compile if A or B
did not have a bigfile constructor? The interface specification is not
needed.
If D supported runtime reflection (and it does to a very very small
degree), then you could use it to ensure the correct constructor is
available.
-Steve
