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digitalmars.D.learn - Circular enum member references in UDAs

reply realhet <real_het hotmail.com> writes:
Hello,

Today I tried to upgrade my sources to the latest LDC, but failed 
with this unfortunate error.

```
import std;

struct S{ E e; }

enum E
{
      S(e2) e1,
      S(e1) e2
}

void main() {
	E.e1.writeln;
}
```

It only runs in DMD 2.086.1 to 2.101.2

I can only think that the compiler changed from two pass lazy 
interpretation down to a single pass.  So when it finds the very 
first attribute " S(e2)" it immediately wants to lookup the 
member e2 and fails.

I really liked this feature because it was so compact. I was able 
to define a state-graph used to parse the structure of almost any 
DLang source files.
This way the structure of the D language can be defined on 1 page 
in D language itself.

[https://ibb.co/HFWR2Qg](https://ibb.co/HFWR2Qg)

Is there a better practice to do this?  All else I can think of 
that the graph-nodes and the graph-edges are declared separately, 
that would be more redundant.  This self-referencing way was the 
only way to declare them in-place.
Feb 15 2024
parent reply Paul Backus <snarwin gmail.com> writes:
On Thursday, 15 February 2024 at 18:12:42 UTC, realhet wrote:

 Hello,

 Today I tried to upgrade my sources to the latest LDC, but 
 failed with this unfortunate error.

 ```
 import std;

 struct S{ E e; }

 enum E
 {
      S(e2) e1,
      S(e1) e2
 }
 ```


Looks like someone reported a similar bug in 2018:

https://issues.dlang.org/show_bug.cgi?id=17656

There was an attempt to fix it, but it looks like the PR author 
wasn't able to get it working correctly in all cases.
Feb 15 2024
parent realhet <real_het hotmail.com> writes:
On Thursday, 15 February 2024 at 20:10:15 UTC, Paul Backus wrote:

 On Thursday, 15 February 2024 at 18:12:42 UTC, realhet wrote:
 There was an attempt to fix it, but it looks like the PR author 
 wasn't able to get it working correctly in all cases.


That means I will solve this by putting the UDAs into a separate 
array.
With a mixin I can still do it without extra redundancy, while 
the compiler enforce the logical correctness of the identifiers.

Thank You for the info.
Feb 15 2024