Variable notation

[Bradley Chatha]

On Sunday, 1 December 2024 at 12:54:27 UTC, Joan wrote:
> Hello, how do i get all the members that are not marked by 
> DO_NOT_CHECK on Check() ?

The following should work:

```d
void Check(T)(T obj) {
     import std.stdio : writeln;
     import std.traits : hasUDA;

     static if (is(T : Object)) {
         auto members = obj.tupleof;
         foreach (i, member; members) {
             static if(hasUDA!(obj.tupleof[i], DO_NOT_CHECK))
                 writeln("DO NOT CHECK: ", i);
             else
                 writeln("CHECK: ", i);
         }
     }
}
```

It may be worth giving `std.traits` a check over, since it has 
other goodies like 
https://dlang.org/phobos/std_traits.html#getSymbolsByUDA

One oddity about D is that UDA information is _very_ easy to 
lose. You'd naturally think that you could do `hasUDA!(member, 
DO_NOT_CHECK)`, but unfortunately `member` no longer contains any 
information about its UDAs - it just becomes a normal `int`, so 
you have to directly index `obj.tupleof` in order to reference 
the original symbol.

You can see this more clearly with the following function:

```d
void Check(T)(T obj) {
     import std.stdio : writeln;
     import std.traits : hasUDA;

     static if (is(T : Object)) {
         auto members = obj.tupleof;
         foreach (i, member; members) {
             pragma(msg, __traits(getAttributes, member));
             pragma(msg, __traits(getAttributes, obj.tupleof[i]));
         }
     }
}
```

Which will print (I added the comments):

```
AliasSeq!() // Member n - using member
AliasSeq!() // Member n - using obj.tupleof
AliasSeq!() // Member x - using member
AliasSeq!() // Member x - using obj.tupleof
AliasSeq!() // Member t - using member
AliasSeq!((DO_NOT_CHECK)) // Member t - using obj.tupleof
```

Hope that helps.