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digitalmars.D.learn - How to declare static compile-time assoc array inside struct?

reply Andrey <saasecondbox yandex.ru> writes:
Hello,
I need to declare a static compile-time assoc array inside struct:
     struct Test
     {
         enum Type : ubyte
         {
             One,
             Two,
             Three
         }

         static immutable string[Type] DESCRIPTION = [Type.One: 
"One!", Type.Two: "It's Two...", Type.Three: "And... Three!"];
     }

I have an error: "non-constant expression". What should I do?

I want to declare it and init at compile-time (to reduce run-time 
overhead). After that it will be used in run-time expressions and 
in compile-time expressions.

Regards, Andrey.
Aug 13 2018
parent reply rikki cattermole <rikki cattermole.co.nz> writes:
On 13/08/2018 11:38 PM, Andrey wrote:

 Hello,
 I need to declare a static compile-time assoc array inside struct:
      struct Test
      {
          enum Type : ubyte
          {
              One,
              Two,
              Three
          }
 
          static immutable string[Type] DESCRIPTION = [Type.One: "One!", 
 Type.Two: "It's Two...", Type.Three: "And... Three!"];
      }
 
 I have an error: "non-constant expression". What should I do?
 
 I want to declare it and init at compile-time (to reduce run-time 
 overhead). After that it will be used in run-time expressions and in 
 compile-time expressions.
 
 Regards, Andrey.


Unsupported. AA's don't go between CT and RT. You must use a module 
constructor to initialize it.
Aug 13 2018
next sibling parent reply Andrey <saasecondbox yandex.ru> writes:
On Monday, 13 August 2018 at 11:53:06 UTC, rikki cattermole wrote:

 Unsupported. AA's don't go between CT and RT. You must use a 
 module constructor to initialize it.


Will be supported in future?
Aug 13 2018
parent Jonathan M Davis <newsgroup.d jmdavisprog.com> writes:
On Monday, August 13, 2018 6:14:56 AM MDT Andrey via Digitalmars-d-learn 
wrote:

 On Monday, 13 August 2018 at 11:53:06 UTC, rikki cattermole wrote:

 Unsupported. AA's don't go between CT and RT. You must use a
 module constructor to initialize it.


 Will be supported in future?


Maybe, but don't plan on it. Stefan Koch is working on a major rewrite for
CTFE (which he calls newCTFE), but it's going to be a while before that's
done (as in, it won't be done this year and has no definitive timeframe for
completion). I don't know if he has plans to improve AA support with newCTFE
(I think that he's mostly focused on getting to the point that it supports
everything that the current CTFE supports but way more efficiently), but
either way, I very much doubt that anyone is going to rework the current
CTFE implementation to support having AAs transfer from compile-time to
runtime. So, while you might get that ability at some point in the future,
for now (and possibly permanently), you will need to proceed without that
ability.

- Jonathan M Davis
Aug 13 2018
prev sibling parent reply Andrey <saasecondbox yandex.ru> writes:
On Monday, 13 August 2018 at 11:53:06 UTC, rikki cattermole wrote:

 You must use a module constructor to initialize it.


Tried this:
static this()
{
     Test.DESCRIPTION = [Test.Type.One: "One!", Test.Type.Two: 
"It's Two...", Test.Type.Three: "And... Three!"];
}

struct Test
{
     // ...
}

I have an error: cannot modify immutable expression DESCRIPTION
Aug 13 2018
next sibling parent Timoses <timosesu gmail.com> writes:
On Monday, 13 August 2018 at 13:21:45 UTC, Andrey wrote:

 On Monday, 13 August 2018 at 11:53:06 UTC, rikki cattermole 
 wrote:

 You must use a module constructor to initialize it.


 Tried this:
 static this()
 {
     Test.DESCRIPTION = [Test.Type.One: "One!", Test.Type.Two: 
 "It's Two...", Test.Type.Three: "And... Three!"];
 }

 struct Test
 {
     // ...
 }

 I have an error: cannot modify immutable expression DESCRIPTION


I suppose something along these lines was meant:

     immutable string[Test.Type] DESCRIPTION;

     shared static this()
     {
         DESCRIPTION = [Test.Type.One: "One!", Test.Type.Two: 
"It's Two...", Test.Type.Three: "And... Three!"];
     }

     struct Test
     {
         enum Type { One, Two, Three };
     }

See also:
https://forum.dlang.org/post/p941qc$43q$1 digitalmars.com
Aug 13 2018
prev sibling next sibling parent Seb <seb wilzba.ch> writes:
On Monday, 13 August 2018 at 13:21:45 UTC, Andrey wrote:

 On Monday, 13 August 2018 at 11:53:06 UTC, rikki cattermole 
 wrote:

 You must use a module constructor to initialize it.


 Tried this:
 static this()
 {
     Test.DESCRIPTION = [Test.Type.One: "One!", Test.Type.Two: 
 "It's Two...", Test.Type.Three: "And... Three!"];
 }

 struct Test
 {
     // ...
 }

 I have an error: cannot modify immutable expression DESCRIPTION


What is your other code?

It can work, e.g.:

https://run.dlang.io/is/kAC4pl
Aug 13 2018
prev sibling parent reply Steven Schveighoffer <schveiguy gmail.com> writes:
On 8/13/18 9:21 AM, Andrey wrote:

 On Monday, 13 August 2018 at 11:53:06 UTC, rikki cattermole wrote:

 You must use a module constructor to initialize it.


 
 Tried this:
 static this()


`shared static this()`

normal static this runs on every thread creation, and so cannot modify 
immutable data.

-Steve
Aug 17 2018
parent Jonathan M Davis <newsgroup.d jmdavisprog.com> writes:
On Friday, August 17, 2018 9:59:18 AM MDT Steven Schveighoffer via 
Digitalmars-d-learn wrote:

 On 8/13/18 9:21 AM, Andrey wrote:

 On Monday, 13 August 2018 at 11:53:06 UTC, rikki cattermole wrote:

 You must use a module constructor to initialize it.


 Tried this:
 static this()


 `shared static this()`

 normal static this runs on every thread creation, and so cannot modify
 immutable data.


Well, it's not _supposed_ to be able to modify immutable data. It's a
long-standing bug that the compiler allows you to initialize immutable
variables in non-shared, static constructors, and if you do it, it's going
to reinitialize it in each thread, which is definitely not good, but for
whatever reason hasn't managed to be enough of a priority to get fixed.

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

So, unfortunately, it's currently up to the programmer to get it right, and
they won't get an error when they screw it up.

- Jonathan M Davis
Aug 17 2018