The following code does not compile:

class Foo { int x; }
class Bar { static Foo f = new Foo(); }  // compiler error
static Foo g = new Foo(); // compiler error
void main() {}

(dmd7) desk3:~/tp/d_test2/dlib>dmd T.d
T.d(4): Error: variable T.Bar.f is mutable. Only const or immutable class thread local variable are allowed, not T.Foo
T.d(5): Error: variable T.g is mutable. Only const or immutable class thread local variable are allowed, not T.Foo

Why aren't static class instances allowed?  Is there a work-around,
or alternative approach to this?

Thanks,

Eric

Eric:

> The following code does not compile:
>
> class Foo { int x; }
> class Bar { static Foo f = new Foo(); }  // compiler error
> static Foo g = new Foo(); // compiler error
> void main() {}
>
> (dmd7) desk3:~/tp/d_test2/dlib>dmd T.d
> T.d(4): Error: variable T.Bar.f is mutable. Only const or immutable class thread local variable are allowed, not T.Foo
> T.d(5): Error: variable T.g is mutable. Only const or immutable class thread local variable are allowed, not T.Foo
>
> Why aren't static class instances allowed?  Is there a work-around,
> or alternative approach to this?

C# compilers present bugs with a standard number, like:

myprog.cs(7,60): error CS1525: .......

This is useful because you can then write an explanation page for each of those bugs, like CS1525:

http://msdn.microsoft.com/en-gb/library/3hdyz4dw%28v=vs.80%29.aspx

In such pages you can explain why Only const or immutable class thread local variable are allowed.

Bye,
bearophile

>> Why aren't static class instances allowed?  Is there a work-around,
>> or alternative approach to this?
>
> C# compilers present bugs with a standard number, like:
>
> myprog.cs(7,60): error CS1525: .......
>
> This is useful because you can then write an explanation page for each of those bugs, like CS1525:
>
> http://msdn.microsoft.com/en-gb/library/3hdyz4dw%28v=vs.80%29.aspx
>
> In such pages you can explain why Only const or immutable class thread local variable are allowed.
>
> Bye,
> bearophile

I'm not sure what you are saying.  Are you implying that not allowing
static class instances is a compiler bug?

-Eric

On Tue, 11 Jun 2013 10:04:21 -0400, Eric <eric@makechip.com> wrote:

>
> The following code does not compile:
>
> class Foo { int x; }
> class Bar { static Foo f = new Foo(); }  // compiler error
> static Foo g = new Foo(); // compiler error

These can be solved with a static ctor.  Essentially, any static initializers must be evaluatable at compile-time.  I know that in the most recent compiler classes have entered this realm, but I don't know the conditions on when they can be used.

The accepted way:

class Bar {
  static Foo f;
  static this() { f = new Foo(); }
}

static Foo g;

static this()
{
   g = new Foo();
}

-Steve

On Tuesday, 11 June 2013 at 16:09:39 UTC, Steven Schveighoffer wrote:
> On Tue, 11 Jun 2013 10:04:21 -0400, Eric <eric@makechip.com> wrote:
>
>>
>> The following code does not compile:
>>
>> class Foo { int x; }
>> class Bar { static Foo f = new Foo(); }  // compiler error
>> static Foo g = new Foo(); // compiler error
>
> These can be solved with a static ctor.  Essentially, any static initializers must be evaluatable at compile-time.  I know that in the most recent compiler classes have entered this realm, but I don't know the conditions on when they can be used.
>
> The accepted way:
>
> class Bar {
>   static Foo f;
>   static this() { f = new Foo(); }
> }
>
> static Foo g;
>
> static this()
> {
>    g = new Foo();
> }
>

Great.  This solved my problem.
Many thanks.

-Eric


> -Steve

> C# compilers present bugs with a standard number, like:
>
> myprog.cs(7,60): error CS1525: .......
>
> This is useful because you can then write an explanation page for each of those bugs, like CS1525:
>
> http://msdn.microsoft.com/en-gb/library/3hdyz4dw%28v=vs.80%29.aspx
>
> In such pages you can explain why Only const or immutable class thread local variable are allowed.

The gentle Simen Kjaeraas has just created an enhancement request:

http://d.puremagic.com/issues/show_bug.cgi?id=10335

Bye,
bearophile