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digitalmars.D - Property access to a struct that contains struct

reply Guenter <gbl1 gmx.net> writes:
Hi,

i do not understand where I am wrong in this code. I seems there 
is a missing constructor, but i have no idea where.


module main;


import std.stdio;


struct A_t
{
   int fvalue;


   A_t opCall()
   {
     return this;
   };

    property  int value () { return fvalue; }

    property void value (int avalue) { fvalue = avalue; }
}


struct B_t
{
   A_t  fext;


   int opCall() { return ext.value; };


    property A_t  ext() { return fext; }

    property void ext(A_t aext) { fext = aext; }
}



void main()
{
   B_t   test;


   test.ext.value = 9;
   int t = test();

   assert ( t == 9);   //  t  is always 0 instead of 9.


   readln();
}


cu
Guenter
Feb 26
next sibling parent reply Eugene Wissner <belka caraus.de> writes:
On Sunday, 26 February 2017 at 11:05:42 UTC, Guenter wrote:
 Hi,

 i do not understand where I am wrong in this code. I seems 
 there is a missing constructor, but i have no idea where.


 module main;


 import std.stdio;


 struct A_t
 {
   int fvalue;


   A_t opCall()
   {
     return this;
   };

    property  int value () { return fvalue; }

    property void value (int avalue) { fvalue = avalue; }
 }


 struct B_t
 {
   A_t  fext;


   int opCall() { return ext.value; };


    property A_t  ext() { return fext; }

    property void ext(A_t aext) { fext = aext; }
 }



 void main()
 {
   B_t   test;


   test.ext.value = 9;
   int t = test();

   assert ( t == 9);   //  t  is always 0 instead of 9.


   readln();
 }


 cu
 Guenter
It should be: property ref A_t ext() { return fext; } you return a copy of A_t and then change this copy instead of the real B_t member.
Feb 26
parent Guenter <gbl1 gmx.net> writes:
On Sunday, 26 February 2017 at 11:15:21 UTC, Eugene Wissner wrote:
 you return a copy of A_t and then change this copy instead of 
 the real B_t member.
Thank you. Guenter
Feb 26
prev sibling parent reply Mike Parker <aldacron gmail.com> writes:
On Sunday, 26 February 2017 at 11:05:42 UTC, Guenter wrote:
 Hi,

 i do not understand where I am wrong in this code. I seems 
 there is a missing constructor, but i have no idea where.
    property A_t  ext() { return fext; }
Structs in D are value types, so you're returning a copy of fext here and that's what's getting updated with the new value. Try this: ref A_T ext() { return fext; }
Feb 26
parent Guenter <gbl1 gmx.net> writes:
On Sunday, 26 February 2017 at 11:18:12 UTC, Mike Parker wrote:
 On Sunday, 26 February 2017 at 11:05:42 UTC, Guenter wrote:
 Hi,

 i do not understand where I am wrong in this code. I seems 
 there is a missing constructor, but i have no idea where.
    property A_t  ext() { return fext; }
Structs in D are value types, so you're returning a copy of fext here and that's what's getting updated with the new value. Try this: ref A_T ext() { return fext; }
Thank you. Guenter
Feb 26