[Issue 24540] New: Add order/index to enum member to return its position

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=24540

          Issue ID: 24540
           Summary: Add order/index to enum member to return its position
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: apz28 at hotmail.com

Currently to get the order/index of an enum member to be done in loop which is
slow. Provide such member will speedup the lookup

enum Foo
{
  one=100, // First order/index=0
  two=399, // Next is 1
  ...
}

auto checkingMember = Foo.two;
size_t index;
foreach (e; EnumMembers!Foo)
{
    if (e == checkingMember)
                return index;
    index++;
}


One of the use case is provide a set of Foo using ubyte/ushort/uint/ulong

struct Set(E)
{
  void set(Foo e)
  {
     v |= 1 << e.order;
  }

  bool isSet(Foo e)
  {
    return (v & (1 << e.order)) != 0;
  }

  More...functions

  uint v;
}

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