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digitalmars.D.learn - RefRange

reply David <d dav1d.de> writes:
It's a RefRange, but not completly ... Can somebody explain me that 
behaviour?

http://dpaste.dzfl.pl/643de2a3
Aug 26 2012
next sibling parent reply =?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:
On 08/26/2012 08:41 AM, David wrote:

 It's a RefRange, but not completly ... Can somebody explain me that
 behaviour?

 http://dpaste.dzfl.pl/643de2a3



According to its documentation, RefRange works differently whether the 
original range is a ForwardRange or not:

   http://dlang.org/phobos/std_range.html#refRange

I have made TestRange a ForwardRange but then I had to comment out two 
lines of your program. Does it work according to your expectations with 
this change?

import std.stdio;
import std.range;

struct TestRange {
     float[] x = [0, 1, 2, 3, 4, 5];

      property bool empty() {
         return x.length == 0;
     }

      property ref float front() {
         return x[0];
     }

     void popFront() {
         //writefln("before: %s", x);
         x = x[1..$];
         //x.popFront();
         //writefln("after: %s", x);
     }

     TestRange save()  property {
         return TestRange(x);
     }
}



void main() {
     static assert(isForwardRange!TestRange);

     TestRange r = TestRange();
     auto rr = refRange(&r);

     //    foreach(element; rr) {}

     //    writefln("Original range: %s", r.x);
     //    writefln("RefRange: %s", rr.x);

     writefln("%s - %s", r.x.ptr, r.x.ptr);

     rr.popFront();

     writefln("%s - %s", r.x.ptr, r.x.ptr);
     writefln("Original range: %s", r.x);
     // We can't expect the RefRange to have the members of the original 
range
     // writefln("RefRange: %s", rr.x);

     r.popFront();

     writefln("%s - %s", r.x.ptr, r.x.ptr);
     writefln("Original range: %s", r.x);
     // We can't expect the RefRange to have the members of the original 
range
     // writefln("RefRange: %s", rr.x);
}

Ali
Aug 26 2012
parent David <d dav1d.de> writes:
Am 26.08.2012 18:06, schrieb Ali Çehreli:

 On 08/26/2012 08:41 AM, David wrote:

 It's a RefRange, but not completly ... Can somebody explain me that
 behaviour?

 http://dpaste.dzfl.pl/643de2a3



 According to its documentation, RefRange works differently whether the
 original range is a ForwardRange or not:

    http://dlang.org/phobos/std_range.html#refRange

 I have made TestRange a ForwardRange but then I had to comment out two
 lines of your program. Does it work according to your expectations with
 this change?

 import std.stdio;
 import std.range;

 struct TestRange {
      float[] x = [0, 1, 2, 3, 4, 5];

       property bool empty() {
          return x.length == 0;
      }

       property ref float front() {
          return x[0];
      }

      void popFront() {
          //writefln("before: %s", x);
          x = x[1..$];
          //x.popFront();
          //writefln("after: %s", x);
      }

      TestRange save()  property {
          return TestRange(x);
      }
 }



 void main() {
      static assert(isForwardRange!TestRange);

      TestRange r = TestRange();
      auto rr = refRange(&r);

      //    foreach(element; rr) {}

      //    writefln("Original range: %s", r.x);
      //    writefln("RefRange: %s", rr.x);

      writefln("%s - %s", r.x.ptr, r.x.ptr);

      rr.popFront();

      writefln("%s - %s", r.x.ptr, r.x.ptr);
      writefln("Original range: %s", r.x);
      // We can't expect the RefRange to have the members of the original
 range
      // writefln("RefRange: %s", rr.x);

      r.popFront();

      writefln("%s - %s", r.x.ptr, r.x.ptr);
      writefln("Original range: %s", r.x);
      // We can't expect the RefRange to have the members of the original
 range
      // writefln("RefRange: %s", rr.x);
 }

 Ali



Yes, that does it, but .save doesn't play well with RefRange (a static 
assert inside RefRange fails, telling that the produced RefRange-Type is 
not a ForwardRange).
Aug 26 2012
prev sibling next sibling parent Jonathan M Davis <jmdavisProg gmx.com> writes:
On Sunday, August 26, 2012 17:41:45 David wrote:

 It's a RefRange, but not completly ... Can somebody explain me that
 behaviour?

 http://dpaste.dzfl.pl/643de2a3



refRange simply returns the original range if it's an input range rather than 
a forward range, since normally, when you have an input range, it isn't a 
value type, and there's no way to copy it, so operating on one reference of it 
is already the same as operating on all of them, making RefRange pointless.

However, you've done the odd thing of declaring a value type input range. I 
don't know why that would ever be done except through ignorance of how ranges 
work. So, refRange is actually returning a copy in your case, which is why 
you're having problems.

And by the way, the only reason that rr.x works is because refRange is 
returning a copy rather than a RefRange!TestRange.

- Jonathan M Davis
Aug 26 2012
prev sibling next sibling parent reply Jonathan M Davis <jmdavisProg gmx.com> writes:
On Sunday, August 26, 2012 10:17:13 Jonathan M Davis wrote:

 On Sunday, August 26, 2012 17:41:45 David wrote:

 It's a RefRange, but not completly ... Can somebody explain me that
 behaviour?
 
 http://dpaste.dzfl.pl/643de2a3



 refRange simply returns the original range if it's an input range rather
 than a forward range, since normally, when you have an input range, it
 isn't a value type, and there's no way to copy it, so operating on one
 reference of it is already the same as operating on all of them, making
 RefRange pointless.
 
 However, you've done the odd thing of declaring a value type input range. I
 don't know why that would ever be done except through ignorance of how
 ranges work. So, refRange is actually returning a copy in your case, which
 is why you're having problems.



Though the fact that you ran into this issue may indicate that having refRange 
return the original if it isn't a forward range was a bad decision. I don't 
know. In the normal case, it's definitely better, because it avoids an 
unnecessary wrapper, but obviously, people can make mistakes. You should still 
be able use RefRange with an input range though, as long as you use it 
directly.

auto wrapped = RefRange!TestRange(&orig);

But it would be better IMHO to just fix it so that your range is a forward 
range, since there's no reason for it not to be.

- Jonathan M Davis
Aug 26 2012
parent reply David <d dav1d.de> writes:
Am 26.08.2012 20:07, schrieb Jonathan M Davis:

 On Sunday, August 26, 2012 10:17:13 Jonathan M Davis wrote:

 On Sunday, August 26, 2012 17:41:45 David wrote:

 It's a RefRange, but not completly ... Can somebody explain me that
 behaviour?

 http://dpaste.dzfl.pl/643de2a3



 refRange simply returns the original range if it's an input range rather
 than a forward range, since normally, when you have an input range, it
 isn't a value type, and there's no way to copy it, so operating on one
 reference of it is already the same as operating on all of them, making
 RefRange pointless.

 However, you've done the odd thing of declaring a value type input range. I
 don't know why that would ever be done except through ignorance of how
 ranges work. So, refRange is actually returning a copy in your case, which
 is why you're having problems.



 Though the fact that you ran into this issue may indicate that having refRange
 return the original if it isn't a forward range was a bad decision. I don't
 know. In the normal case, it's definitely better, because it avoids an
 unnecessary wrapper, but obviously, people can make mistakes. You should still
 be able use RefRange with an input range though, as long as you use it
 directly.

 auto wrapped = RefRange!TestRange(&orig);

 But it would be better IMHO to just fix it so that your range is a forward
 range, since there's no reason for it not to be.

 - Jonathan M Davis



Ranges died another time for me. This refRange copy thingy cost me lots 
of time, then I tried to implement a .save method, which uhm, just 
didn't work together with RefRange (isForwardRange!T succeeded, but 
isForwardRange!(RefRange!T) failed).

Anyways, thanks for your explanations!
Aug 26 2012
parent reply =?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:
On 08/26/2012 02:21 PM, David wrote:


 I tried to implement a .save method, which uhm, just
 didn't work together with RefRange (isForwardRange!T succeeded, but
 isForwardRange!(RefRange!T) failed).



What version of dmd? What is the code?

When I add the following lines to the beginning of main() of the program 
that I have used in my other post, they both pass:

     static assert(isForwardRange!TestRange);
     static assert(isForwardRange!(RefRange!TestRange));

Ali
Aug 26 2012
parent reply David <d dav1d.de> writes:
Am 26.08.2012 23:33, schrieb Ali Çehreli:

 On 08/26/2012 02:21 PM, David wrote:

  > I tried to implement a .save method, which uhm, just
  > didn't work together with RefRange (isForwardRange!T succeeded, but
  > isForwardRange!(RefRange!T) failed).

 What version of dmd? What is the code?

 When I add the following lines to the beginning of main() of the program
 that I have used in my other post, they both pass:

      static assert(isForwardRange!TestRange);
      static assert(isForwardRange!(RefRange!TestRange));

 Ali



DMD 2.059 and: 
https://github.com/Dav1dde/BraLa/blob/7440688038bfd50a06fd9a49b8e9b6d08c7b4c28/brala/utils/queue.d

But I don't care anylonger, I rewrote the whole Queue class (now it's a 
"real" queue, e.g. you can wait until all items are used up, with 
core.sync.condtion), I also don't feel like wasting more time in ranges, 
when I don't need them.
Aug 26 2012
parent reply David <d dav1d.de> writes:
Sorry, dmd 2.060
Aug 26 2012
parent =?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:
On 08/26/2012 02:46 PM, David wrote:

 Sorry, dmd 2.060



Hmmm. I use 2.060 as well.

Ali
Aug 26 2012
prev sibling next sibling parent "Era Scarecrow" <rtcvb32 yahoo.com> writes:
On Sunday, 26 August 2012 at 18:07:27 UTC, Jonathan M Davis wrote:

 But it would be better IMHO to just fix it so that your range 
 is a forward range, since there's no reason for it not to be.



  That brings up my own question. I'm writing an application that 
will end up using an output range (likely an appender, so 
semi-dynamic). How will I be sure that what's passed to other 
functions will append to the range? And more importantly, if I 
use save and then rewrite an earlier section (due to updated 
information) would that also be correct assuming memory didn't 
change on it? Can you give an example?

  Currently my code goes something like this:

  struct ... {
   innerType[] someInnerType;

   void write(T)(T outputRange)
   if(isForwardRange!(T)){

    auto firstBlock = outputRange.save;
    //write to outputRange, first output will be re-written
    writeFirstBlock(outputRange);

    foreach(ref i; someInnerType) {
     i.write(outputRange);
    }

    //updated information for first block
    writeFirstBlock(save);
   }
  }
Aug 26 2012
prev sibling next sibling parent "Jonathan M Davis" <jmdavisProg gmx.com> writes:
On Sunday, August 26, 2012 23:20:49 Era Scarecrow wrote:

 On Sunday, 26 August 2012 at 18:07:27 UTC, Jonathan M Davis wrote:

 But it would be better IMHO to just fix it so that your range
 is a forward range, since there's no reason for it not to be.



 That brings up my own question. I'm writing an application that
 will end up using an output range (likely an appender, so
 semi-dynamic). How will I be sure that what's passed to other
 functions will append to the range? And more importantly, if I
 use save and then rewrite an earlier section (due to updated
 information) would that also be correct assuming memory didn't
 change on it? Can you give an example?
 
 Currently my code goes something like this:
 
 struct ... {
 innerType[] someInnerType;
 
 void write(T)(T outputRange)
 if(isForwardRange!(T)){
 
 auto firstBlock = outputRange.save;
 //write to outputRange, first output will be re-written
 writeFirstBlock(outputRange);
 
 foreach(ref i; someInnerType) {
 i.write(outputRange);
 }
 
 //updated information for first block
 writeFirstBlock(save);
 }
 }



I don't think that I really understand the question, but I'd be worried about 
intermixing save with operating on a range as an output range. It _should_ 
work, but save was designed with reading in mind, not writing. An output range 
doesn't have to have save or even front or popFront. All it needs is to work 
with put. Output ranges are a very different beast from input ranges, even if 
input ranges can be output ranges.

That being said, I'd expect that save would save the current state, and any 
writing to the original would not affect the saved range.

- Jonathan M Davis
Aug 27 2012
prev sibling parent "Era Scarecrow" <rtcvb32 yahoo.com> writes:
On Monday, 27 August 2012 at 20:46:18 UTC, Jonathan M Davis wrote:

 I don't think that I really understand the question, but I'd be 
 worried about intermixing save with operating on a range as an 
 output range. It _should_ work, but save was designed with 
 reading in mind, not writing. An output range doesn't have to 
 have save or even front or popFront. All it needs is to work 
 with put. Output ranges are a very different beast from input 
 ranges, even if input ranges can be output ranges.

 That being said, I'd expect that save would save the current 
 state, and any writing to the original would not affect the 
 saved range.



  Well the first block actually holds size information and the 
information it holds is the old information, stuff may have been 
added or taken away, so hopefully not to have to do two passes (a 
dummy pass and then a real one) I was hoping save would save the 
location. If it doesn't reference the previous location using the 
current data then I'll need to figure something out.

  It's this that's been holding off one of my projects for a while 
as I'm not sure how to best approach it.
Aug 27 2012