Opaque type (struct) with a static immutable fails to compile without constructor - why?

[Simen Kjærås]

On Thursday, 4 March 2021 at 13:58:48 UTC, frankp wrote:
> Hi all,
>
> I want to make an opaque type that simply contains an integer 
> with some immutable constants and toString pretty printing. 
> Like this:
>
> struct Foo_t
> {
>    private long foo;
>    alias foo this;
>    static immutable long Inf = long.max; //1)
>
>    void toString(...){}
> }
>
> On dmd 2.092.1 this fails with:
>   1) Error: cannot implicitly convert expression 9223...L of 
> type immutable(long) to Foo_t
>
> I simply want to initialize an immutable long with long.max.
> Why the conversion to Foo_t ?
>
> If I add a constructor:
> private this(long f)
> {
>    foo = f;
> }
>
> It compiles but according to code coverage this constructor is 
> never called.
> What's going on?

I tried compiling your code locally on DMD 2.094.1, and had no 
issues. Again with 2.095.0, no issues. On run.dlang.io, with all 
dmd compilers from 2.060, and it just plain works.

Now, that's after removing ... from toString. With that present, 
it fails with some variation of 'Error: undefined identifier 
'__va_list_tag''.

Most likely, you have shortened your program for clarity, and 
removed the issue you're experiencing in the process. Can we have 
another one, with the issue still there?

--
   Simen