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digitalmars.D.learn - String switch is odd using betterC

reply Abby <loniro7678 twit-mail.com> writes:
I have a simple enum of strings like so:

enum Alphabet : string
{
     a = "A",
     b = "B",
     c = "C",
     d = "D",
     e = "E",
     f = "F",
     g = "G"
}

and then simple final switch like so:

extern(C) void main()
{
     auto s = Alphabet.f;
     final switch(s)
     {
         case Alphabet.a: break;
         case Alphabet.b: break;
         case Alphabet.c: break;
         case Alphabet.d: break;
         case Alphabet.e: break;
         case Alphabet.f: break;
         case Alphabet.g: break;
     }
}

The problem I have is that this causes:

/dlang/dmd/linux/bin64/../../src/druntime/import/object.d(2999): 
Error: TypeInfo cannot be used with -betterC

Odd think is that wehen I remove g from my enum it compiles just 
fine, so it seems that this compilation error occurs only when my 
enum has more then 6 members.

Any idea why?
Feb 26 2020
next sibling parent Abby <loniro7678 twit-mail.com> writes:
On Wednesday, 26 February 2020 at 08:25:00 UTC, Abby wrote:

 /dlang/dmd/linux/bin64/../../src/druntime/import/object.d(2999): Error:
TypeInfo cannot be used with -betterC

 Odd think is that wehen I remove g from my enum it compiles 
 just fine, so it seems that this compilation error occurs only 
 when my enum has more then 6 members.

 Any idea why?


Ok so this is enough to reproduce the problem

extern(C) void main()
{
     auto s = "F";
     final switch(s)
     {
         case "A": break;
         case "B": break;
         case "C": break;
         case "D": break;
         case "E": break;
         case "F": break;
         case "G": break;
     }
}
Feb 26 2020
prev sibling parent reply Abby <loniro7678 twit-mail.com> writes:
On Wednesday, 26 February 2020 at 08:25:00 UTC, Abby wrote:

 Any idea why?


Ok so this is enough to produce the same result, it seems that 
there is a problem in string switch when there is more the 6 
cases.

extern(C) void main()
{
     auto s = "F";
     final switch(s)
     {
         case "A": break;
         case "B": break;
         case "C": break;
         case "D": break;
         case "E": break;
         case "F": break;
         case "G": break;
     }
}
Feb 26 2020
next sibling parent Petar Kirov [ZombineDev] <petar.p.kirov gmail.com> writes:
On Wednesday, 26 February 2020 at 08:32:50 UTC, Abby wrote:

 On Wednesday, 26 February 2020 at 08:25:00 UTC, Abby wrote:

 Any idea why?


 Ok so this is enough to produce the same result, it seems that 
 there is a problem in string switch when there is more the 6 
 cases.

 extern(C) void main()
 {
     auto s = "F";
     final switch(s)
     {
         case "A": break;
         case "B": break;
         case "C": break;
         case "D": break;
         case "E": break;
         case "F": break;
         case "G": break;
     }
 }


This looks like a possible cause:
https://github.com/dlang/druntime/blob/e018a72084e54ecc7466e97c96e4557b96b7f905/src/core/internal/switch_.d#L34
Feb 26 2020
prev sibling parent Simen =?UTF-8?B?S2rDpnLDpXM=?= <simen.kjaras gmail.com> writes:
On Wednesday, 26 February 2020 at 08:32:50 UTC, Abby wrote:

 On Wednesday, 26 February 2020 at 08:25:00 UTC, Abby wrote:

 Any idea why?


 Ok so this is enough to produce the same result, it seems that 
 there is a problem in string switch when there is more the 6 
 cases.

 extern(C) void main()
 {
     auto s = "F";
     final switch(s)
     {
         case "A": break;
         case "B": break;
         case "C": break;
         case "D": break;
         case "E": break;
         case "F": break;
         case "G": break;
     }
 }


The explanation can be found in 
druntime/import/core/internal/switch_.d: the __switch template 
does a simple binary search for less than 7 cases, but calls 
.idup on each case label for >= 7 cases.

There's a comment there about why it's being done, but it seems 
to be a far more complicated fix than necessary - static 
immutable cases = [caseLabels]; works just as well, it seems.

Anyway, the current code was added in this commit: 
https://github.com/dlang/druntime/commit/fa665f6618af7dbc09ed5ba1333f385017b7ece8.

Anyways, reported here: 
https://issues.dlang.org/show_bug.cgi?id=20613

--
   Simen
Feb 26 2020