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digitalmars.D.learn - Is this a bug in dmd 2.067 for struct initializers?

reply "stewarth" <growlercab gmail.com> writes:
Hi All,

This works under dmd 2066.1 but fails under dmd 2.067-b2.

---
struct A {
     int val;
}

static immutable A[] someA = [{val:1}, {val:2}];

struct B {
     A* a;
}

static immutable B[] someB = [{a:&someA[0]}, {a:&someA[1]}];

void main()
{

     writefln("a:%s", someA);
     writefln("b:%s", someB);
}
---
Error under DMD 2.067-b2:

hack.d(27): Error: cannot use non-constant CTFE pointer in an 
initializer '&[A(1), A(2)][0]'
hack.d(27): Error: cannot use non-constant CTFE pointer in an 
initializer '&[A(1), A(2)][1]'


Is this a bug, or a deliberate change?

I'm thinking a bug because I want it to initialize at runtime 
before main(). I don't actually want any CTFE stuff here.

Thanks,
stew
Feb 18 2015
parent reply =?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:
On 02/18/2015 10:39 PM, stewarth wrote:


 This works under dmd 2066.1 but fails under dmd 2.067-b2.


I don't know whether it is a bug.


 struct B {
      A* a;


In any case, that must be immutable(A)*.


 }

 static immutable B[] someB = [{a:&someA[0]}, {a:&someA[1]}];



 I want it to initialize at runtime before main(). I don't
 actually want any CTFE stuff here.


Then you need 'static this()' (or 'shared static this()'):

static immutable B[] someB;

static this() {
     someB = [ B(&someA[0]), B(&someA[1]) ];
}

Note that I could not use the named member syntax because in my case the 
compiler cannot know what the right-hand side expression is. However, it 
is still possible with a temporary where the type is explicit as in your 
case:

static this() {
     immutable B[] tmp = [ {a:&someA[0]}, {a:&someA[1]} ];
     someB = tmp;
}

Ali
Feb 18 2015
parent reply "stewarth" <growlercab gmail.com> writes:
On Thursday, 19 February 2015 at 07:46:51 UTC, Ali Çehreli wrote:

 On 02/18/2015 10:39 PM, stewarth wrote:


 This works under dmd 2066.1 but fails under dmd 2.067-b2.


 I don't know whether it is a bug.


 struct B {
      A* a;


 In any case, that must be immutable(A)*.


 }

 static immutable B[] someB = [{a:&someA[0]}, {a:&someA[1]}];



 I want it to initialize at runtime before main(). I don't
 actually want any CTFE stuff here.


 Then you need 'static this()' (or 'shared static this()'):

 static immutable B[] someB;

 static this() {
     someB = [ B(&someA[0]), B(&someA[1]) ];
 }

 Note that I could not use the named member syntax because in my 
 case the compiler cannot know what the right-hand side 
 expression is. However, it is still possible with a temporary 
 where the type is explicit as in your case:

 static this() {
     immutable B[] tmp = [ {a:&someA[0]}, {a:&someA[1]} ];
     someB = tmp;
 }

 Ali


Hi Ali,

Thanks for the help.

I've gone with "static this()" approach and it works. In a way 
it's cleaner because it's explicit that these variables are only 
initialised at runtime before d_main(). At least that's how I 
understand things :)

It would be nice if the named syntax also worked in static 
this(), maybe I'll file an ER for it. I'm a big fan of the whole 
named args thing in Python, which from a quick search has been 
discussed before in the forums.


Cheers,
Stew
Feb 19 2015
parent reply "Martin Nowak" <code dawg.eu> writes:
On Thursday, 19 February 2015 at 22:07:55 UTC, stewarth wrote:

 I've gone with "static this()" approach and it works.


You should use shared static this to initialize immutable 
variables.
Feb 22 2015
next sibling parent reply =?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:
On 02/22/2015 03:17 PM, Martin Nowak wrote:

 On Thursday, 19 February 2015 at 22:07:55 UTC, stewarth wrote:

 I've gone with "static this()" approach and it works.


 You should use shared static this to initialize immutable variables.


Is that because they are not thread-local? If so, initializing the same 
variable in multiple 'static this()' blocks would indeed be a race 
condition. Very important...

Ali
Feb 22 2015
parent Jonathan M Davis via Digitalmars-d-learn writes:
On Sunday, February 22, 2015 17:45:48 Ali Çehreli via Digitalmars-d-learn wrote:

 On 02/22/2015 03:17 PM, Martin Nowak wrote:

 On Thursday, 19 February 2015 at 22:07:55 UTC, stewarth wrote:

 I've gone with "static this()" approach and it works.


 You should use shared static this to initialize immutable variables.


 Is that because they are not thread-local? If so, initializing the same
 variable in multiple 'static this()' blocks would indeed be a race
 condition. Very important...


Yeah. It really should be illegal to initialize immutable variables in
non-shared static constructors.

https://issues.dlang.org/show_bug.cgi?id=4923

- Jonathan M Davis
Feb 23 2015
prev sibling parent reply "amber" <amber.swan gmail.com> writes:
On Sunday, 22 February 2015 at 23:17:33 UTC, Martin Nowak wrote:

 On Thursday, 19 February 2015 at 22:07:55 UTC, stewarth wrote:

 I've gone with "static this()" approach and it works.


 You should use shared static this to initialize immutable 
 variables.


OK, thanks a lot for the help.

Cheers,
Stew
Feb 22 2015
parent reply "stewarth" <growlercab gmail.com> writes:
On Monday, 23 February 2015 at 02:10:09 UTC, amber wrote:

 On Sunday, 22 February 2015 at 23:17:33 UTC, Martin Nowak wrote:

 On Thursday, 19 February 2015 at 22:07:55 UTC, stewarth wrote:

 I've gone with "static this()" approach and it works.


 You should use shared static this to initialize immutable 
 variables.


 OK, thanks a lot for the help.

 Cheers,
 Stew


Oops, replied under my friends account ... sorry for the 
confusion.

I am assuming this is only if I have more than one thread?

Thanks,
Stew
Feb 22 2015
parent reply ketmar <ketmar ketmar.no-ip.org> writes:
On Mon, 23 Feb 2015 02:15:08 +0000, stewarth wrote:


 On Monday, 23 February 2015 at 02:10:09 UTC, amber wrote:

 On Sunday, 22 February 2015 at 23:17:33 UTC, Martin Nowak wrote:

 On Thursday, 19 February 2015 at 22:07:55 UTC, stewarth wrote:

 I've gone with "static this()" approach and it works.


 You should use shared static this to initialize immutable variables.


 OK, thanks a lot for the help.

 Cheers,
 Stew


=20
 Oops, replied under my friends account ... sorry for the confusion.
=20
 I am assuming this is only if I have more than one thread?


do not count on that. even if *you* never create additional threads, any=20
library can. it's better to always remember that you don't control all=20
execution pathes then be sorry later.=
Feb 22 2015
parent "stewarth" <growlercab gmail.com> writes:
On Monday, 23 February 2015 at 04:04:08 UTC, ketmar wrote:

 On Mon, 23 Feb 2015 02:15:08 +0000, stewarth wrote:


 On Monday, 23 February 2015 at 02:10:09 UTC, amber wrote:

 On Sunday, 22 February 2015 at 23:17:33 UTC, Martin Nowak 
 wrote:

 On Thursday, 19 February 2015 at 22:07:55 UTC, stewarth 
 wrote:

 I've gone with "static this()" approach and it works.


 You should use shared static this to initialize immutable 
 variables.


 OK, thanks a lot for the help.

 Cheers,
 Stew


 
 Oops, replied under my friends account ... sorry for the 
 confusion.
 
 I am assuming this is only if I have more than one thread?


 do not count on that. even if *you* never create additional 
 threads, any
 library can. it's better to always remember that you don't 
 control all
 execution pathes then be sorry later.


Ah yes of course. Good point and thanks for the help.

Stew
Feb 22 2015