http://d.puremagic.com/issues/show_bug.cgi?id=4425

           Summary: More bells & whistles for bitfields
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: Phobos
        AssignedTo: nobody@puremagic.com
        ReportedBy: bearophile_hugs@eml.cc


--- Comment #0 from bearophile_hugs@eml.cc 2010-07-04 12:39:29 PDT ---
When bit fields are used to define bit protocols etc., they sometimes have constant fields, or already initialized variable fields. So It can be positive for std.bitmanip.bitfields to support that too, this is an example:

          field1 : 1;
          field2 : 2 = 0b01;
immutable field3 : 3;
immutable field4 : 4 = 0b1110;


As with normal immutable fields in structs, the language has to forbid the write on immutable fields. Probably in many cases the compiler can't enforce this at compile time on bit fields (because of the type system granularity; something similar happens with pointers to single bits in bit-arrays), so probably the bit field immutability needs to be enforced at run-time (maybe even in release mode too, because it's a hard constraint).

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--- Comment #1 from bearophile_hugs@eml.cc 2010-09-24 18:47:19 PDT ---
See also bug 4937

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--- Comment #2 from bearophile_hugs@eml.cc 2010-10-04 18:16:44 PDT ---
Another possible feature is to make std.bitmanip.bitfields generate two versions of the code, that get compiled conditionally according to the CPU endianess:


static if (std.system.endian == std.system.Endian.BigEndian) {
    ...
} else {
    ...
}

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Era Scarecrow <rtcvb32@yahoo.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
                 CC|                            |rtcvb32@yahoo.com
         AssignedTo|nobody@puremagic.com        |rtcvb32@yahoo.com


--- Comment #3 from Era Scarecrow <rtcvb32@yahoo.com> 2012-08-02 22:02:41 PDT ---
Adding const to a field seems pretty easy; specifically the setter is simply left out of the template. So as a final proposed usage, it would look like:

 mixin(bitfields(
          int,  "named",           4,
    const int,  "c_named",         4,
          uint, "named_def=5",     4,    //includes defaulted value of 5
    const uint, "c_named_def=10",  4));  //defaulted value of 10


 bitfieldsOn is being worked on, and effectively works identically to bitfields
except you specify a variable you want to use; Default values won't work well
with it however.

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--- Comment #4 from bearophile_hugs@eml.cc 2012-08-03 03:06:07 PDT ---
(In reply to comment #3)
> Adding const to a field seems pretty easy; specifically the setter is simply left out of the template.

OK.


> So as a final proposed usage, it would look like:
> 
>  mixin(bitfields(
>           int,  "named",           4,
>     const int,  "c_named",         4,
>           uint, "named_def=5",     4,    //includes defaulted value of 5
>     const uint, "c_named_def=10",  4));  //defaulted value of 10

Good. And what do you think about facing the endianess problems (Comment 2)?


>  bitfieldsOn is being worked on, and effectively works identically to bitfields
> except you specify a variable you want to use; Default values won't work well
> with it however.

What's bitfieldsOn?

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