Why this doesn't compile?

http://dpaste.dzfl.pl/21ef5b04

class Foo {}

struct Bar1 {
	const(Foo[]) member;	
}

struct Bar2 {
	const Foo member;	
}

void main() {
	const Bar1 bar1;
	const Bar2 bar2;
	Bar1 b1 = bar1; // ok
	Bar2 b2 = bar2; // cannot implicitly convert expression (bar2) of type const(Bar2) to Bar2
}

Am 14.10.2013 13:35, schrieb Jack Applegame:
> Why this doesn't compile?
>
> http://dpaste.dzfl.pl/21ef5b04
>
> class Foo {}
>
> struct Bar1 {
>      const(Foo[]) member;
> }
>
> struct Bar2 {
>      const Foo member;
> }
>
> void main() {
>      const Bar1 bar1;
>      const Bar2 bar2;
>      Bar1 b1 = bar1; // ok
>      Bar2 b2 = bar2; // cannot implicitly convert expression (bar2) of
> type const(Bar2) to Bar2
> }

Because in D const is transitive. That means if a reference is const the object it points to is also const. And everything that object points to is const, and so on.

The line "Bar2 b2 = bar2;" would remove const from "member" which does not happen because const is not convertible to mutable implicitly.

Kind Regards
Benjamin Thaut

On Monday, 14 October 2013 at 11:38:23 UTC, Benjamin Thaut wrote:
> The line "Bar2 b2 = bar2;" would remove const from "member"
Seems strange, because b2.member is const by declaration.

On Monday, 14 October 2013 at 11:45:30 UTC, Jack Applegame wrote:
> On Monday, 14 October 2013 at 11:38:23 UTC, Benjamin Thaut wrote:
>> The line "Bar2 b2 = bar2;" would remove const from "member"
> Seems strange, because b2.member is const by declaration.

Strange indeed and smells like a bug. `auto bar = Bar2(bar2.member)` works so it should be assignable.

Am 14.10.2013 13:54, schrieb Dicebot:
> On Monday, 14 October 2013 at 11:45:30 UTC, Jack Applegame wrote:
>> On Monday, 14 October 2013 at 11:38:23 UTC, Benjamin Thaut wrote:
>>> The line "Bar2 b2 = bar2;" would remove const from "member"
>> Seems strange, because b2.member is const by declaration.
>
> Strange indeed and smells like a bug. `auto bar = Bar2(bar2.member)`
> works so it should be assignable.

d.puremagic.com/issues/show_bug.cgi?id=9665

On Monday, 14 October 2013 at 11:35:32 UTC, Jack Applegame wrote:
> Why this doesn't compile?
>
> http://dpaste.dzfl.pl/21ef5b04
>
> class Foo {}
>
> struct Bar1 {
> 	const(Foo[]) member;	
> }
>
> struct Bar2 {
> 	const Foo member;	
> }
>
> void main() {
> 	const Bar1 bar1;
> 	const Bar2 bar2;
> 	Bar1 b1 = bar1; // ok
> 	Bar2 b2 = bar2; // cannot implicitly convert expression (bar2) of type const(Bar2) to Bar2
> }

This is compilable using git head.

On Monday, 14 October 2013 at 13:56:58 UTC, Benjamin Thaut wrote:
> Am 14.10.2013 13:54, schrieb Dicebot:
>> On Monday, 14 October 2013 at 11:45:30 UTC, Jack Applegame wrote:
>>> On Monday, 14 October 2013 at 11:38:23 UTC, Benjamin Thaut wrote:
>>>> The line "Bar2 b2 = bar2;" would remove const from "member"
>>> Seems strange, because b2.member is const by declaration.
>>
>> Strange indeed and smells like a bug. `auto bar = Bar2(bar2.member)`
>> works so it should be assignable.
>
> d.puremagic.com/issues/show_bug.cgi?id=9665

I don't see how this is related to the topic.

Am 14.10.2013 16:19, schrieb Maxim Fomin:
> On Monday, 14 October 2013 at 13:56:58 UTC, Benjamin Thaut wrote:
>> Am 14.10.2013 13:54, schrieb Dicebot:
>>> On Monday, 14 October 2013 at 11:45:30 UTC, Jack Applegame wrote:
>>>> On Monday, 14 October 2013 at 11:38:23 UTC, Benjamin Thaut wrote:
>>>>> The line "Bar2 b2 = bar2;" would remove const from "member"
>>>> Seems strange, because b2.member is const by declaration.
>>>
>>> Strange indeed and smells like a bug. `auto bar = Bar2(bar2.member)`
>>> works so it should be assignable.
>>
>> d.puremagic.com/issues/show_bug.cgi?id=9665
>
> I don't see how this is related to the topic.

I thought maybe its related to this bug.

On Monday, 14 October 2013 at 14:18:10 UTC, Maxim Fomin wrote:
> On Monday, 14 October 2013 at 11:35:32 UTC, Jack Applegame wrote:
>> Why this doesn't compile?
>>
>> http://dpaste.dzfl.pl/21ef5b04
>>
>> class Foo {}
>>
>> struct Bar1 {
>> 	const(Foo[]) member;	
>> }
>>
>> struct Bar2 {
>> 	const Foo member;	
>> }
>>
>> void main() {
>> 	const Bar1 bar1;
>> 	const Bar2 bar2;
>> 	Bar1 b1 = bar1; // ok
>> 	Bar2 b2 = bar2; // cannot implicitly convert expression (bar2) of type const(Bar2) to Bar2
>> }
>
> This is compilable using git head.

Recently I found a small compiler bug.
http://d.puremagic.com/issues/show_bug.cgi?id=11187

And, a week ago it is fixed. 2.064 beta1 contains the fix.

Kenji Hara

On 10/14/2013 10:33 AM, Kenji Hara wrote:

> On Monday, 14 October 2013 at 14:18:10 UTC, Maxim Fomin wrote:

>> This is compilable using git head.

When I read that line ...

> Kenji Hara

... I was thinking about that person. :)

Thank you Kenji!

Ali