Open source dmd on Reddit!

[Charles Hixson]

Andrei Alexandrescu wrote:
> Michel Fortin wrote:
>> On 2009-03-06 14:35:59 -0500, Walter Bright 
>> <newshound1 at digitalmars.com> said:
>>
>>> Andrei Alexandrescu wrote:
>>>> "Can't live without bitfields! Give me bitfields and I'll lift the 
>>>> Earth!"
>>>>
>>>> "Here they are, std.bitmanip. Well-defined and more portable and 
>>>> flexible than C's."
>>>>
>>>> "Meh, don't like the definition syntax."
>>>
>>> Classic.
>>
>> Well, he certainly has a point. Compare this:
>>
>>     mixin(bitfields!(
>>         uint, "x",    2,
>>         int,  "y",    3,
>>         uint, "z",    2,
>>         bool, "flag", 1));
>>
>> With this:
>>
>>     uint x : 2;
>>     int  y : 3;
>>     uint z : 2;
>>     bool flag : 1;
>>
>> The second is certainly prettier and more readable.
> 
> (Just to clarify: to me the humor of the situation was that someone who 
> considered bitfields an absolute prerequisite for language adoption 
> subsequently found the syntax excuse to bail out. Essentially the 
> hypothetical user was fabricating one pretext after another to 
> rationalize their pre-made decision to not try D -- an absolute classic 
> attitude when it comes about acquiring new programming languages.)
> 
> About the syntax itself - definitions are few and uses are many. In 
> addition the D solution:
> 
> (a) guarantees data layout;
> 
> (b) offers symbolic limits, e.g. x_max and x_min are automatically added 
> as enums;
> 
> (c) checks for overflow, which is essential for small bitfields;
> 
> (d) offers a way to manipulate the fields wholesale by using the 
> concatenation of all their names, e.g. xyzflag;
> 
> (e) suggests that there are other cool things that can be done within 
> the language, not by adding features to it.
> 
> Hopefully that makes up for the more loaded syntax.
> 
>> Does it matter much? Not to me; I rarely use bit fields. If I were 
>> using them a lot, perhaps I'd be more concerned.
> 
> I am using them here and there - even in Phobos - and they work very well.
> 
>> While I don't care very much about bitfields, that "mixin(tmpl!(...))" 
>> syntax is awful. "mixin tmpl!(...)" is better, but has too many 
>> limitations, and it isn't always clear for the user which one should 
>> be used. Couldn't D2 get a better syntax for mixins?
> 
> I agree it should.
> 
> 
> Andrei
I'm glad that they're there.  And I'm glad that they work.  But I really 
hate the syntax, and am glad I've never needed to use them.  MUCH better 
would have been:
mixin(bitfields!("
      uint, x,    2,
      int,  y,    3,
      uint, z,    2,
      bool, flag, 1
      ")

even better would have been:
mixin(bitfields!("
      uint x :  2,
      int  y :  3,
      uint z :  2,
      bool flag : 1
      ")

The bitfield battle isn't one I'm involved with, and I rarely comment on 
syntax...but this is, to my mind, a much nicer syntax.  Moving the quote 
marks to a pre-existing boundary location and removing them internally 
is a large gain.  There is a small further gain in specifying the 
bit-field as a type-name : length string.  The colon is a slightly 
better delimiter to use here than the comma, as the comma is being used 
as the separator between individual bit field specifications.  A further 
gain is that it's more similar to a form already known by many people.

I'm not a compiler writer, so I don't know if this would have been 
difficult.  I just know that looking at it *I* find it much more 
readable.  Another step might have been to allow the entire string to 
end with a comma, thus:
mixin(bitfields!("
      uint x :  2,
      int  y :  3,
      uint z :  2,
      bool flag : 1,
      ")
so that it would be easier to shuffle the fields during development. 
This has it's pluses and minuses, but by and large I think it's optional 
presence would be a benefit.