• Rufus Smith (14/14) Jul 21 2016 I would like to combine two types
• =?UTF-8?Q?Ali_=c3=87ehreli?= (17/30) Jul 21 2016 Bitfields may actually be useful in this case:
• Rufus Smith (5/41) Jul 21 2016 Maybe... I don't like extra member. Bitfields seem like it would
• =?UTF-8?Q?Ali_=c3=87ehreli?= (22/45) Jul 21 2016 A factory function can help:
• Johannes Pfau (5/20) Jul 22 2016 To be pedantic about this: The initializers actually do overlap. As A

Rufus Smith <RufusSmith indi.com> writes:

I would like to combine two types


template Foo(A, B = 4)
{
     union
     {
        byte b = B;
        int a = A << 8;
     }
}

This packs a and b together in to an int bytes, saving an 
int(rather than storing a and b in an int each) and makes it 
easier to access.

I get an error about overlapping default initialization. They 
don't actually overlap in this case because of the shift.

=?UTF-8?Q?Ali_=c3=87ehreli?= <acehreli yahoo.com> writes:

On 07/21/2016 06:48 PM, Rufus Smith wrote:
 I would like to combine two types


 template Foo(A, B = 4)
 {
      union
      {
         byte b = B;
         int a = A << 8;
      }
 }

 This packs a and b together in to an int bytes, saving an int(rather
 than storing a and b in an int each) and makes it easier to access.

Bitfields may actually be useful in this case:

   https://dlang.org/phobos/std_bitmanip.html#.bitfields

 I get an error about overlapping default initialization. They don't
 actually overlap in this case because of the shift.

The following at least compiles:

struct Foo(int A, byte B = 4)
{
     union
     {
         byte b = void;
         int a = void;
         uint __both = (A << 8) | B;
     }
}

void main() {
     auto f = Foo!(42)();
}

Ali

Rufus Smith <RufusSmith indi.com> writes:

On Friday, 22 July 2016 at 02:08:06 UTC, Ali Çehreli wrote:
 On 07/21/2016 06:48 PM, Rufus Smith wrote:
 I would like to combine two types


 template Foo(A, B = 4)
 {
      union
      {
         byte b = B;
         int a = A << 8;
      }
 }

 This packs a and b together in to an int bytes, saving an

 int(rather
 than storing a and b in an int each) and makes it easier to

 access.

 Bitfields may actually be useful in this case:

   https://dlang.org/phobos/std_bitmanip.html#.bitfields

They don't allow default assignment though?

 I get an error about overlapping default initialization. They

 don't
 actually overlap in this case because of the shift.

 The following at least compiles:

 struct Foo(int A, byte B = 4)
 {
     union
     {
         byte b = void;
         int a = void;
         uint __both = (A << 8) | B;
     }
 }

 void main() {
     auto f = Foo!(42)();
 }

 Ali

Maybe... I don't like extra member. Bitfields seem like it would 
be the best way but I require default initialization. I want to 
hide as details of the work on unpacking as possible.

=?UTF-8?Q?Ali_=c3=87ehreli?= <acehreli yahoo.com> writes:

On 07/21/2016 08:00 PM, Rufus Smith wrote:

 Bitfields may actually be useful in this case:

   https://dlang.org/phobos/std_bitmanip.html#.bitfields

 They don't allow default assignment though?

A factory function can help:

import std.bitmanip;

struct S(int a_init, byte b_init) {
     mixin (bitfields!(int, "a", 24,
                       byte, "b", 8));
      disable this();
}

auto makeS(int a_init, byte b_init = 4)() {
     auto s = S!(a_init, b_init).init;
     s.a = a_init;
     s.b = b_init;
     return s;
}

void main() {
     const s = makeS!42();
     assert(s.a == 42);
     assert(s.b == 4);
}

 The following at least compiles:

 struct Foo(int A, byte B = 4)
 {
     union
     {
         byte b = void;
         int a = void;
         uint __both = (A << 8) | B;
     }
 }

 void main() {
     auto f = Foo!(42)();
 }

 Ali

 Maybe... I don't like extra member.

Me neither. Besides, 'b' coincides with a different part of 'a' 
depending on the endianness of the system.

Ali

Johannes Pfau <nospam example.com> writes:

Am Fri, 22 Jul 2016 01:48:52 +0000
schrieb Rufus Smith <RufusSmith indi.com>:

 I would like to combine two types
 
 
 template Foo(A, B = 4)
 {
      union
      {
         byte b = B;
         int a = A << 8;
      }
 }
 
 
 I get an error about overlapping default initialization. They 
 don't actually overlap in this case because of the shift.

To be pedantic about this: The initializers actually do overlap. As A
<< 8 shifts in zeroes, these bits are initialized as well. I think
there's no idiomatic way to initialize only part of an integer.