Consider:

import std.stdio;

class A
{
    final print() { writeln(this); } // no return type
}

class B : A
{
    final void print() { writeln(this); }
}

void main()
{
    auto b = new B;
    b.print();

    A a1 = b;
    a1.print();

    A a2 = new A;
    a2.print();
}

That compiles:

$ dmd -de -w -g ./main.d
$ main
main.B
main.B
main.A

with dmd 2.074 on linux:

$ dmd --version
DMD64 D Compiler v2.074.0
Copyright (c) 1999-2017 by Digital Mars written by Walter Bright

Is that a bug? (in the compiler). I'm learning D, and I'm half way through Andrei's book; I also read the documentation (on D's website) and I think that shouldn't compile?

V Wed, 03 May 2017 06:54:15 +0000
nkm1 via Digitalmars-d-learn <digitalmars-d-learn@puremagic.com>
napsáno:

> Consider:
> 
> import std.stdio;
> 
> class A
> {
>      final print() { writeln(this); } // no return type
> }
> 
> class B : A
> {
>      final void print() { writeln(this); }
> }
> 
> void main()
> {
>      auto b = new B;
>      b.print();
> 
>      A a1 = b;
>      a1.print();
> 
>      A a2 = new A;
>      a2.print();
> }
> 
> That compiles:
> 
> $ dmd -de -w -g ./main.d
> $ main
> main.B
> main.B
> main.A
> 
> with dmd 2.074 on linux:
> 
> $ dmd --version
> DMD64 D Compiler v2.074.0
> Copyright (c) 1999-2017 by Digital Mars written by Walter Bright
> 
> Is that a bug? (in the compiler). I'm learning D, and I'm half way through Andrei's book; I also read the documentation (on D's website) and I think that shouldn't compile?

print in A is template:

import std.stdio;

class A
{
    template print() {
        void print()
        {
            writeln("A version");
        } // no return type
    }
}

class B : A
{
     final void print() { writeln("B version"); }
}

void main()
{
     auto b = new B;
     b.print();

     A a1 = b;
     a1.print();

     A a2 = new A;
     a2.print();
}

// output:
B version
A version
A version

On 2017-05-03 08:54, nkm1 wrote:
> Consider:
>
> import std.stdio;
>
> class A
> {
>      final print() { writeln(this); } // no return type
> }
>
> class B : A
> {
>      final void print() { writeln(this); }
> }
>
> void main()
> {
>      auto b = new B;
>      b.print();
>
>      A a1 = b;
>      a1.print();
>
>      A a2 = new A;
>      a2.print();
> }
>
> That compiles:
>
> $ dmd -de -w -g ./main.d
> $ main
> main.B
> main.B
> main.A
>
> with dmd 2.074 on linux:
>
> $ dmd --version
> DMD64 D Compiler v2.074.0
> Copyright (c) 1999-2017 by Digital Mars written by Walter Bright
>
> Is that a bug? (in the compiler). I'm learning D, and I'm half way
> through Andrei's book; I also read the documentation (on D's website)
> and I think that shouldn't compile?

It might be by accident but I think the compiler is inferring the return type. Just as "auto" is not necessary to infer the type of a variable if there's another attribute:

auto a = 3;
const auto b = 4; // here "auto" is redundant
const c = 5;

In your case you have "final" as the attribute.

-- 
/Jacob Carlborg

On Wednesday, 3 May 2017 at 07:37:31 UTC, Jacob Carlborg wrote:
> It might be by accident but I think the compiler is inferring the return type. Just as "auto" is not necessary to infer the type of a variable if there's another attribute:
>
> auto a = 3;
> const auto b = 4; // here "auto" is redundant
> const c = 5;
>
> In your case you have "final" as the attribute.

Yes, the compiler is inferring the return type. However, it _should_ be inferring it as void, and the override in B should then be illegal. If I stick

    pragma(msg, typeof(print));

right after each declaration for print, then it prints

@system void()

for A and

void()

for B, which is odd, since both should be @system. Interestingly, if both have pragmas at the same time, _then_ I get a compilation error:

qd.d(11): Error: function qd.B.print cannot override final function qd.A.print

So, I'd say that there's definitely a bug here.

On Wednesday, 3 May 2017 at 08:10:04 UTC, Jonathan M Davis wrote:
> So, I'd say that there's definitely a bug here.

https://issues.dlang.org/show_bug.cgi?id=17366

On Wednesday, 3 May 2017 at 06:54:15 UTC, nkm1 wrote:
> final method type inference stuff

Jacob and Jonathan - thank you, this is clear to me now. Hopefully it will get fixed at some point.

On Wednesday, 3 May 2017 at 07:34:03 UTC, Daniel Kozák wrote:
>
> print in A is template:
>

What :)
How does it interact with 'final'?

V Wed, 03 May 2017 09:21:47 +0000
nkm1 via Digitalmars-d-learn <digitalmars-d-learn@puremagic.com>
napsáno:

> On Wednesday, 3 May 2017 at 07:34:03 UTC, Daniel Kozák wrote:
> >
> > print in A is template:
> > 
> 
> What :)
> How does it interact with 'final'?

final is not important here

V Wed, 03 May 2017 09:21:47 +0000
nkm1 via Digitalmars-d-learn <digitalmars-d-learn@puremagic.com>
napsáno:

> On Wednesday, 3 May 2017 at 07:34:03 UTC, Daniel Kozák wrote:
> >
> > print in A is template:
> > 
> 
> What :)
> How does it interact with 'final'?

hmm obviously it is problem only with final

On Wednesday, 3 May 2017 at 07:34:03 UTC, Daniel Kozák wrote:
> V Wed, 03 May 2017 06:54:15 +0000
> nkm1 via Digitalmars-d-learn <digitalmars-d-learn@puremagic.com>
> napsáno:
>
>> Consider:
>> 
>> import std.stdio;
>> 
>> class A
>> {
>>      final print() { writeln(this); } // no return type
>> }
>> 
>> class B : A
>> {
>>      final void print() { writeln(this); }
>> }
>> 
>> void main()
>> {
>>      auto b = new B;
>>      b.print();
>> 
>>      A a1 = b;
>>      a1.print();
>> 
>>      A a2 = new A;
>>      a2.print();
>> }
>> 
>> That compiles:
>> 
>> $ dmd -de -w -g ./main.d
>> $ main
>> main.B
>> main.B
>> main.A
>> 
>> with dmd 2.074 on linux:
>> 
>> $ dmd --version
>> DMD64 D Compiler v2.074.0
>> Copyright (c) 1999-2017 by Digital Mars written by Walter Bright
>> 
>> Is that a bug? (in the compiler). I'm learning D, and I'm half way through Andrei's book; I also read the documentation (on D's website) and I think that shouldn't compile?
>
> print in A is template:
>
> import std.stdio;
>
> class A
> {
>     template print() {
>         void print()
>         {
>             writeln("A version");
>         } // no return type
>     }
> }

How is it a template in the original example?

final print() { writeln(this); } // no return type

does not have the extra set of parens required to turn it into a template. It _does_ use inference, just like

static a = 42;

uses inference and

final auto print() { writeln(this); }

uses inference, but it shouldn't be a template any more than

static a = 42;

is a template.

- Jonathan M Davis