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digitalmars.D.bugs - [Issue 5714] New: case ranges in final switches

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=5714

           Summary: case ranges in final switches
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: bearophile_hugs eml.cc



This is a low-priority enhancement suggestion.

If the type to final-switch on has a natural ordering (so it's not an enum!),
like a char/ubyte/byte, then in some situations I'd like to use the range
syntax:


void main() {
     ubyte u;
     final switch (u) {
         case   0: .. case 100: break;
         case 101: .. case 255: break;
     }
}


Currently DMD 2.052 gives the errors:
test.d(4): Error: case ranges not allowed in final switch
test.d(5): Error: case ranges not allowed in final switch


See also bug 5713

If case ranges are not allowed on full-range int values, then you can't use
them in a final switch.

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next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=5714


Andrej Mitrovic <andrej.mitrovich gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |andrej.mitrovich gmail.com



05:55:57 PST ---


 If case ranges are not allowed on full-range int values, then you can't use
 them in a final switch.


Basically the compiler just translates this:

case 1: .. case 3: call()

into:

case 1:
case 2:
case 3:
    call()

And it also limits the number of cases to 256 (for optimization purposes?).

So a final switch would only work on byte-types. I'm not sure if Walter would
like a feature that only works with one fundamental type. Note also that
because `final switch` currently works on ints (personally I would reject such
code), people would assume they could add case ranges for the full int type,
but they would get the 256 case limitation error instead.

As a current workaround you could use a mixin that generates the case
statements and a 'default' which throws a SwitchError.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=5714







 So a final switch would only work on byte-types. I'm not sure if Walter would
 like a feature that only works with one fundamental type.


There are also chars, and ubytes.



 `final switch` currently works on ints (personally I would reject such
 code),


It's indeed wrong, there is another enhancement request/bug report that asks
for it to be fixed!



 As a current workaround you could use a mixin that generates the case
 statements and a 'default' which throws a SwitchError.


You can't have a default in static switches.

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prev sibling parent d-bugmail puremagic.com writes:
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06:34:36 PST ---



 

 So a final switch would only work on byte-types. I'm not sure if Walter would
 like a feature that only works with one fundamental type.


 
 There are also chars, and ubytes.


They have the same range so it doesn't matter what you call them, the range is
limited to 0 .. 255.


 You can't have a default in static switches.


Yes, you would use a normal switch for that. But you could have a helper
template mixin that could error internally if you don't provide all the cases,
which is a workaround for final switches not providing case ranges.

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