Re: Template method in interfaces
On 8/10/16 12:41 PM, Arafel wrote: I have to say that the fact that this compiles at all seems like a bug to me according to [1], even more so that the method in A is called: That is definitely a bug. D ignores many misplaced attributes, but not override. -Steve
Re: Template method in interfaces
On Wednesday, 10 August 2016 at 15:52:29 UTC, Lodovico Giaretta
wrote:
On Wednesday, 10 August 2016 at 15:48:10 UTC, Lodovico Giaretta
wrote:
On Wednesday, 10 August 2016 at 15:39:19 UTC, Arafel wrote:
Would it even make sense to "force" (deprecation warning) a
"final" keyword in any implicitly-final function (I wasn't
even aware of those, I have to admit)? It would make things
much clearer, like with "override"...
I read the spec again, and found out that it says interfaces
cannot contain templated functions... So either my
interpretation is the intended one and the spec is outdated,
or the spec is right and the compiler is bugged.
Anyway what I said about implicit final is true for classes. In
classes, I don't like the idea of having to put an explicit
final, but this is debatable. For interfaces, I'm ok with
forcing an explicit final attribute (but as I said the spec
does not allow templated functions in interfaces, even if the
compiler does).
I have to say that the fact that this compiles at all seems like
a bug to me according to [1], even more so that the method in A
is called:
---
import std.stdio;
public class A {
public void func(T)(T t) {
writeln("Within A");
}
}
public class B : A {
override public void func(T)(T t) {
writeln("Within B");
}
}
void main() {
A a = new B();
a.func(1);
}
---
https://dpaste.dzfl.pl/f3d5beff2e51
If the function is "final", even if implicitly so, the "override"
should fail according to the spec as I, and I guess 99% of the
people[2], understand it.
[1]: https://dlang.org/spec/function.html#virtual-functions
[2]: OK, technically not, since it just says that "Functions
marked as final may not be overridden in a derived class [...]"
and this function is not *marked* as final, but implicitly
final... still...
Re: Template method in interfaces
On Wednesday, 10 August 2016 at 15:54:42 UTC, Adam D. Ruppe wrote: On Wednesday, 10 August 2016 at 15:48:10 UTC, Lodovico Giaretta wrote: I read the spec again, and found out that it says interfaces cannot contain templated functions... So either my interpretation is the intended one and the spec is outdated, or the spec is right and the compiler is bugged. Spec must be out of date, I remember this being a conscious decision to add them. Last line of this page: https://dlang.org/spec/template.html#limitations I'll file a bug report for this and an enhancement request for implicit final in interfaces.
Re: Template method in interfaces
On Wednesday, 10 August 2016 at 15:48:10 UTC, Lodovico Giaretta wrote: I read the spec again, and found out that it says interfaces cannot contain templated functions... So either my interpretation is the intended one and the spec is outdated, or the spec is right and the compiler is bugged. Spec must be out of date, I remember this being a conscious decision to add them.
Re: Template method in interfaces
On Wednesday, 10 August 2016 at 15:48:10 UTC, Lodovico Giaretta wrote: On Wednesday, 10 August 2016 at 15:39:19 UTC, Arafel wrote: Would it even make sense to "force" (deprecation warning) a "final" keyword in any implicitly-final function (I wasn't even aware of those, I have to admit)? It would make things much clearer, like with "override"... I read the spec again, and found out that it says interfaces cannot contain templated functions... So either my interpretation is the intended one and the spec is outdated, or the spec is right and the compiler is bugged. Anyway what I said about implicit final is true for classes. In classes, I don't like the idea of having to put an explicit final, but this is debatable. For interfaces, I'm ok with forcing an explicit final attribute (but as I said the spec does not allow templated functions in interfaces, even if the compiler does).
Re: Template method in interfaces
On Wednesday, 10 August 2016 at 15:39:19 UTC, Arafel wrote: On Wednesday, 10 August 2016 at 15:25:40 UTC, Lodovico Giaretta wrote: Because templated functions cannot be virtual, it follows that I.func is final. Having no body, the compiler thinks that its body will be found by the linker in another object file, but this does not happen, so the linker complains. Being I.func final, C.func just hides it, so you would not incur any problem if you called func explicitly on an object of type C. So what you found is not a bug, but some unintuitive behaviour due to templated functions being implicitly final and forward declarations. Maybe the compiler should emit a warning about implicitly-final functions in interfaces. Would it even make sense to "force" (deprecation warning) a "final" keyword in any implicitly-final function (I wasn't even aware of those, I have to admit)? It would make things much clearer, like with "override"... I read the spec again, and found out that it says interfaces cannot contain templated functions... So either my interpretation is the intended one and the spec is outdated, or the spec is right and the compiler is bugged.
Re: Template method in interfaces
On Wednesday, 10 August 2016 at 15:25:40 UTC, Lodovico Giaretta wrote: Because templated functions cannot be virtual, it follows that I.func is final. Having no body, the compiler thinks that its body will be found by the linker in another object file, but this does not happen, so the linker complains. Being I.func final, C.func just hides it, so you would not incur any problem if you called func explicitly on an object of type C. So what you found is not a bug, but some unintuitive behaviour due to templated functions being implicitly final and forward declarations. Maybe the compiler should emit a warning about implicitly-final functions in interfaces. Would it even make sense to "force" (deprecation warning) a "final" keyword in any implicitly-final function (I wasn't even aware of those, I have to admit)? It would make things much clearer, like with "override"...
Re: Template method in interfaces
On Wednesday, 10 August 2016 at 15:20:37 UTC, Arafel wrote:
I'm not sure if the following is even expected to work, since
I'm not sure how the vtable for the interface would look like
(well, that would be applicable to any overriden templated
method, though):
---
public interface I {
void func(T)(T t);
}
public class C : I {
void func(T)(T t) {
}
}
void main() {
I i = new C();
i.func(1);
}
---
But since the error I get is in the linker, and not in the
compiler, I guess that's somehow a bug? Or how should it work
then?
https://dpaste.dzfl.pl/7a14fa074673
/d31/f76.o: In function `_Dmain':
/d31/f76.d:(.text._Dmain+0x24): undefined reference to
`_D3f761I11__T4funcTiZ4funcMFiZv' collect2: error: ld returned
1 exit status --- errorlevel 1
PS: Now I see [1] that it shouldn't, so perhaps the compiler
should reject templated methods in interfaces from the
beginning?
[1]: http://forum.dlang.org/post/jg504s$1f7t$1...@digitalmars.com
Because templated functions cannot be virtual, it follows that
I.func is final. Having no body, the compiler thinks that its
body will be found by the linker in another object file, but this
does not happen, so the linker complains.
Being I.func final, C.func just hides it, so you would not incur
any problem if you called func explicitly on an object of type C.
So what you found is not a bug, but some unintuitive behaviour
due to templated functions being implicitly final and forward
declarations. Maybe the compiler should emit a warning about
implicitly-final functions in interfaces.
Template method in interfaces
I'm not sure if the following is even expected to work, since I'm
not sure how the vtable for the interface would look like (well,
that would be applicable to any overriden templated method,
though):
---
public interface I {
void func(T)(T t);
}
public class C : I {
void func(T)(T t) {
}
}
void main() {
I i = new C();
i.func(1);
}
---
But since the error I get is in the linker, and not in the
compiler, I guess that's somehow a bug? Or how should it work
then?
https://dpaste.dzfl.pl/7a14fa074673
/d31/f76.o: In function `_Dmain': /d31/f76.d:(.text._Dmain+0x24):
undefined reference to `_D3f761I11__T4funcTiZ4funcMFiZv'
collect2: error: ld returned 1 exit status --- errorlevel 1
PS: Now I see [1] that it shouldn't, so perhaps the compiler
should reject templated methods in interfaces from the beginning?
[1]: http://forum.dlang.org/post/jg504s$1f7t$1...@digitalmars.com
