• Jiyan (15/15) Jul 30 2017 Hey,
• Eugene Wissner (8/23) Jul 30 2017 this(this) is called after the struct is copied. Doing something
• Jiyan (2/27) Jul 30 2017 Ok thank you :)
• Moritz Maxeiner (14/29) Jul 30 2017 I'll assume you mean copying (as per the title) not moving

Jiyan <jiyan jiyan.info> writes:

Hey,
just wanted to know whether something like this would be possible 
sowmehow:

struct S
{
int m;
int n;
this(this)
{
m = void;
n = n;
}
}

So not the whole struct is moved everytime f.e. a function is 
called, but only n has to be "filled"

Eugene Wissner <belka caraus.de> writes:

On Sunday, 30 July 2017 at 19:22:07 UTC, Jiyan wrote:
 Hey,
 just wanted to know whether something like this would be 
 possible sowmehow:

 struct S
 {
 int m;
 int n;
 this(this)
 {
 m = void;
 n = n;
 }
 }

 So not the whole struct is moved everytime f.e. a function is 
 called, but only n has to be "filled"

this(this) is called after the struct is copied. Doing something 
in the postblit constructor is too late. The second thing is that 
the struct is copied with memcpy. What you propose would require 
2 memcpy calls to copy the first part of the struct and then the 
second part. Besides it is difficult to implement, it may reduce 
the performance of the copying since memcpy is optimized to copy 
memory chunks.

Jiyan <jiyan jiyan.info> writes:

On Sunday, 30 July 2017 at 19:32:48 UTC, Eugene Wissner wrote:
 On Sunday, 30 July 2017 at 19:22:07 UTC, Jiyan wrote:
 Hey,
 just wanted to know whether something like this would be 
 possible sowmehow:

 struct S
 {
 int m;
 int n;
 this(this)
 {
 m = void;
 n = n;
 }
 }

 So not the whole struct is moved everytime f.e. a function is 
 called, but only n has to be "filled"

 this(this) is called after the struct is copied. Doing 
 something in the postblit constructor is too late. The second 
 thing is that the struct is copied with memcpy. What you 
 propose would require 2 memcpy calls to copy the first part of 
 the struct and then the second part. Besides it is difficult to 
 implement, it may reduce the performance of the copying since 
 memcpy is optimized to copy memory chunks.

Ok thank you :)

Moritz Maxeiner <moritz ucworks.org> writes:

On Sunday, 30 July 2017 at 19:22:07 UTC, Jiyan wrote:
 Hey,
 just wanted to know whether something like this would be 
 possible sowmehow:

 struct S
 {
 int m;
 int n;
 this(this)
 {
 m = void;
 n = n;
 }
 }

 So not the whole struct is moved everytime f.e. a function is 
 called, but only n has to be "filled"

I'll assume you mean copying (as per the title) not moving 
(because moving doesn't make sense to me in this context); use a 
dedicated method:

struct S
{
     int m, n;
     S sparseDup()
     {
         S obj;
         obj.n = n;
         return obj;
     }
}