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digitalmars.D - foreach over pointer to range

reply Artur Skawina <art.08.09 gmail.com> writes:
"foreach (e; pointer_to_range)" currently fails with:

   Error: foreach: Range* is not an aggregate type

It can be worked around with 

   struct RangePtr(R) {
      R* ptr;
      alias ptr this;
       property front()() { return ptr.front; }
   }

but this adds unnecessary overhead (unfortunately such struct is not
always treated the same as a real pointer, eg when passing it around).

Is there some reason that makes the is-aggregate check necessary, or could
it be dropped?


Thanks,

artur
Jun 05 2012
parent reply Timon Gehr <timon.gehr gmx.ch> writes:
On 06/05/2012 08:42 PM, Artur Skawina wrote:

 "foreach (e; pointer_to_range)" currently fails with:

     Error: foreach: Range* is not an aggregate type

 It can be worked around with

     struct RangePtr(R) {
        R* ptr;
        alias ptr this;
         property front()() { return ptr.front; }
     }

 but this adds unnecessary overhead (unfortunately such struct is not
 always treated the same as a real pointer, eg when passing it around).

 Is there some reason that makes the is-aggregate check necessary, or could
 it be dropped?


 Thanks,

 artur


It should be dropped. A pointer to range is a perfectly fine range.
Jun 05 2012
next sibling parent reply "Peter Alexander" <peter.alexander.au gmail.com> writes:
On Tuesday, 5 June 2012 at 18:46:51 UTC, Timon Gehr wrote:

 On 06/05/2012 08:42 PM, Artur Skawina wrote:

 "foreach (e; pointer_to_range)" currently fails with:

    Error: foreach: Range* is not an aggregate type

 It can be worked around with...




Why not: foreach(e; *pointer_to_range)

Seems like the obvious solution to me, and works.
Jun 05 2012
parent Artur Skawina <art.08.09 gmail.com> writes:
On 06/05/12 21:25, Peter Alexander wrote:

 On Tuesday, 5 June 2012 at 18:46:51 UTC, Timon Gehr wrote:

 On 06/05/2012 08:42 PM, Artur Skawina wrote:

 "foreach (e; pointer_to_range)" currently fails with:

    Error: foreach: Range* is not an aggregate type

 It can be worked around with...




 
 Why not: foreach(e; *pointer_to_range)
 
 Seems like the obvious solution to me, and works.


Works by copying the whole range struct, which is what I don't
want to happen. And no, using a class is not an option. :)

artur
Jun 05 2012
prev sibling parent reply simendsjo <simendsjo gmail.com> writes:
On Tue, 05 Jun 2012 20:46:51 +0200, Timon Gehr <timon.gehr gmx.ch> wrote:


 It should be dropped. A pointer to range is a perfectly fine range.



Sure..? I couldn't get it to work either:
struct R {
     string test = "aoeu";
      property front() { return test[0]; }
      property bool empty() { return !test.length; }
     void popFront(){test = test[0..$];}
}

void main() {
     R r;
     R* p = &r;
     foreach(ch; p) // invalid foreach aggregate p
         writeln(ch);
}
Jun 05 2012
parent reply Artur Skawina <art.08.09 gmail.com> writes:
On 06/05/12 22:23, simendsjo wrote:

 On Tue, 05 Jun 2012 20:46:51 +0200, Timon Gehr <timon.gehr gmx.ch> wrote:
 

 It should be dropped. A pointer to range is a perfectly fine range.


 
 
 Sure..? I couldn't get it to work either:
 struct R {
     string test = "aoeu";
      property front() { return test[0]; }
      property bool empty() { return !test.length; }
     void popFront(){test = test[0..$];}
 }
 
 void main() {
     R r;
     R* p = &r;
     foreach(ch; p) // invalid foreach aggregate p
         writeln(ch);
 }


It /is/ a valid range, but it's /not/ currently accepted
by foreach.

So you have to write the above as:
   
   struct R {
       string test = "aoeu";
        property front() { return test[0]; }
        property bool empty() { return !test.length; }
       void popFront(){test = test[0..$];}
   }

   struct RangePtr(R) {
      R* ptr;
      alias ptr this;
       property front()() { return ptr.front; }
   }

   void main() {
       R r;
       auto p = RangePtr!R(&r);
       foreach(ch; p)
           writeln(ch);
   }

which works, but only obfuscates the code and can be less efficient.

artur
Jun 05 2012
parent reply simendsjo <simendsjo gmail.com> writes:
On Tue, 05 Jun 2012 22:38:22 +0200, Artur Skawina <art.08.09 gmail.com>  
wrote:


 On 06/05/12 22:23, simendsjo wrote:

 On Tue, 05 Jun 2012 20:46:51 +0200, Timon Gehr <timon.gehr gmx.ch>  
 wrote:


 It should be dropped. A pointer to range is a perfectly fine range.



 Sure..? I couldn't get it to work either:
 struct R {
     string test = "aoeu";
      property front() { return test[0]; }
      property bool empty() { return !test.length; }
     void popFront(){test = test[0..$];}
 }

 void main() {
     R r;
     R* p = &r;
     foreach(ch; p) // invalid foreach aggregate p
         writeln(ch);
 }


 It /is/ a valid range, but it's /not/ currently accepted
 by foreach.


(...)

 which works, but only obfuscates the code and can be less efficient.

 artur


Well, then it's not a *perfectly fine* range, is it then :)
Jun 05 2012
parent Artur Skawina <art.08.09 gmail.com> writes:
On 06/05/12 22:41, simendsjo wrote:

 On Tue, 05 Jun 2012 22:38:22 +0200, Artur Skawina <art.08.09 gmail.com> wrote:
 

 On 06/05/12 22:23, simendsjo wrote:

 On Tue, 05 Jun 2012 20:46:51 +0200, Timon Gehr <timon.gehr gmx.ch> wrote:


 It should be dropped. A pointer to range is a perfectly fine range.



 Sure..? I couldn't get it to work either:
 struct R {
     string test = "aoeu";
      property front() { return test[0]; }
      property bool empty() { return !test.length; }
     void popFront(){test = test[0..$];}
 }

 void main() {
     R r;
     R* p = &r;
     foreach(ch; p) // invalid foreach aggregate p
         writeln(ch);
 }


 It /is/ a valid range, but it's /not/ currently accepted
 by foreach.


 (...)

 which works, but only obfuscates the code and can be less efficient.


 
 Well, then it's not a *perfectly fine* range, is it then :)


It *is* a perfectly fine range; the problem is with 'foreach'.

artur
Jun 05 2012