• user001 (45/45) Feb 19 2016 Well struct don't have it, but i would like something like it but
• cym13 (31/76) Feb 19 2016 Indeed, that's very cumbersome, and that's why "alias this" was
• user001 (1/1) Feb 19 2016 Yes that's exactly what i needed, thanks!
• Yuxuan Shui (19/23) Feb 19 2016 How about

user001 <youdontneedthis dont.com> writes:

Well struct don't have it, but i would like something like it but 
only for data, i don't need functions or anything like that just 
data.


     struct A
     {
         int valueA;
     }

     struct B
     {
         A a;
         int valueB;
     }

     struct C
     {
         B b;
         int valueC;
     }

     C c;

     c.b.a.valueA; // not elegant

     B* b = &c.b;

     b.a.valueA; // we can access A


     // alternative 
--------------------------------------------------

     struct A
     {
         int valueA;
     }

     struct B
     {
         int valueB;
     }

     struct C
     {
         A a;
         B b;
         int valueC;
     }

     C c;

     c.a.valueA; // a bit more elegant but still not very, 
c.valueA would be prefered

     B* b = &c.b;

     b.? // can't access A, unless we do some hack that assumes B 
always follows A in the definition


Is there any way to do inheritance with structs, is there a 
reason why we can't extend structures like in C++?

cym13 <cpicard openmailbox.org> writes:

On Friday, 19 February 2016 at 21:58:24 UTC, user001 wrote:
 Well struct don't have it, but i would like something like it 
 but only for data, i don't need functions or anything like that 
 just data.


     struct A
     {
         int valueA;
     }

     struct B
     {
         A a;
         int valueB;
     }

     struct C
     {
         B b;
         int valueC;
     }

     C c;

     c.b.a.valueA; // not elegant

     B* b = &c.b;

     b.a.valueA; // we can access A


     // alternative 
 --------------------------------------------------

     struct A
     {
         int valueA;
     }

     struct B
     {
         int valueB;
     }

     struct C
     {
         A a;
         B b;
         int valueC;
     }

     C c;

     c.a.valueA; // a bit more elegant but still not very, 
 c.valueA would be prefered

     B* b = &c.b;

     b.? // can't access A, unless we do some hack that assumes 
 B always follows A in the definition


 Is there any way to do inheritance with structs, is there a 
 reason why we can't extend structures like in C++?

Indeed, that's very cumbersome, and that's why "alias this" was 
introduced! It allows you to subtype: calls to members or methods 
that do not belong the the main type are forwarded to the member. 
Unfortunately we don't have multiple alias this so you can only 
forward to one member but it isn't very problematic in practice 
as otherwise things are likely to become easy to abuse.

Use it like that:

     import std.stdio;

     struct A
     {
         int valueA = 1;
     }

     struct B
     {
         A a;
         alias a this;

         int valueB = 2;
     }


     struct C
     {
         B b;
         alias b this;

         int valueC = 3;
     }

     void main(string[] args) {
         C c;

         assert(c.valueA == 1);
         assert(c.valueB == 2);
         assert(c.valueC == 3);
     }

user001 <youdontneedthis dont.com> writes:

Yes that's exactly what i needed, thanks!

Yuxuan Shui <yshuiv7 gmail.com> writes:

On Friday, 19 February 2016 at 21:58:24 UTC, user001 wrote:
 Well struct don't have it, but i would like something like it 
 but only for data, i don't need functions or anything like that 
 just data.

 [...]

How about

struct A
{
     int valueA;
}

struct B
{
     A a;
     int valueB;
     alias a this;
}

struct C
{
     B b;
     int valueC;
     alias b this;
}

?