I really can't wrap my head around these. I fought whole day
trying to figure out how to do the simplest thing one can
imagine: remove an element from a doubly linked list. Here's what
I've tried, see if there is a recurring mistake of thought or
something:

import std.stdio;
import std.algorithm;
import std.range;
import std.container;

struct Point {
     int x;
     int y;
}

void main() {
     DList!Point points;
     points.insert(Point(0,0));
     points.insert(Point(10,10));
     points.insert(Point(5,5));
     points.insert(Point(20,20));

     points.remove(takeOne(find!(p => p.x > 7)(points[])));
     // test.d(18): Error: function
std.container.DList!(Point).DList.remove (Range r) is not
callable using argument types (Result)

     points.linearRemove(takeOne(find!(p => p.x > 7)(points[])));
     // test.d(21): Error: template
std.container.DList!(Point).DList.linearRemove cannot deduce
function from argument types !()(Result), candidates are:
     // /usr/include/dmd/phobos/std/container.d(2234):
std.container.DList!(Point).DList.linearRemove(R)(R r) if (is(R
== Range))
     // /usr/include/dmd/phobos/std/container.d(2240):
std.container.DList!(Point).DList.linearRemove(R)(R r) if (is(R
== Range))
     // /usr/include/dmd/phobos/std/container.d(2253):
std.container.DList!(Point).DList.linearRemove(R)(R r) if (is(R
== Take!Range))

     points.remove(find!(p => p.x > 7)(points[]));
     // 0

     points.remove(takeOne(filter!(p => p.x > 7)(points[])));
     // test.d(30): Error: function
std.container.DList!(Point).DList.remove (Range r) is not
callable using argument types (Result)

     points.remove(filter!(p => p.x > 7)(points[]));
     // test.d(33): Error: function
std.container.DList!(Point).DList.remove (Range r) is not
callable using argument types (FilterResult!(__lambda3, Range))

     points.linearRemove(filter!(p => p.x > 7)(points[]));
     // test.d(36): Error: template
std.container.DList!(Point).DList.linearRemove cannot deduce
function from argument types !()(FilterResult!(__lambda1,
Range)), candidates are:
     // /usr/include/dmd/phobos/std/container.d(2234):
std.container.DList!(Point).DList.linearRemove(R)(R r) if (is(R
== Range))
     // /usr/include/dmd/phobos/std/container.d(2240):
std.container.DList!(Point).DList.linearRemove(R)(R r) if (is(R
== Range))
     // /usr/include/dmd/phobos/std/container.d(2253):
std.container.DList!(Point).DList.linearRemove(R)(R r) if (is(R
== Take!Range))

     foreach (Point p; points) {
         if (p.x > 7) {
             //points.remove(/* Somehow get the range */);
             break;
         }
     }

     foreach (Point p; points) {
         writeln(p.x);
     }
}


Purpose is to remove one element that matches predicate, or any
amount really. Now DList.remove is defined as "Range remove(Range
r)" and filter is "auto filter(Range)(Range rs) if
(isInputRange!(Unqual!Range))" with explanation "The call
filter!(predicate)(range) returns a new range only containing
elements x in range for which predicate(x) is true." So if I
understand correctly, filter should return a range that I can
remove from the list. Why isn't this working?

Text went nuts at least for me so here's raw pastebin of it
http://pastebin.com/raw.php?i=JfLFdsNj

Ok, I got it working with

points.linearRemove(find!(p => p.x > 7)(points[]).take(1));

I thought takeOne would work and didn't thought of trying take(1), but I guess not. I also learned that containers don't accept filter results as a range so no problem, I can accept that. Still, feels quite complicated. I hope it's worth it in the long run :)

newguy:

> Still, feels quite complicated. I hope it's worth it in the long run :)

It is complicated. Other parts of Phobos are both less complex and more useful. This means you have chosen a bad part of Phobos :-)

Bye,
bearophile

On Friday, 7 March 2014 at 19:53:04 UTC, newguy wrote:
> I really can't wrap my head around these. I fought whole day
> trying to figure out how to do the simplest thing one can
> imagine: remove an element from a doubly linked list. Here's what
> I've tried, see if there is a recurring mistake of thought or
> something:
>
> import std.stdio;
> import std.algorithm;
> import std.range;
> import std.container;
>
> struct Point {
>      int x;
>      int y;
> }
>
> void main() {
>      DList!Point points;
>      points.insert(Point(0,0));
>      points.insert(Point(10,10));
>      points.insert(Point(5,5));
>      points.insert(Point(20,20));
>
>      points.remove(takeOne(find!(p => p.x > 7)(points[])));
>      // test.d(18): Error: function
> std.container.DList!(Point).DList.remove (Range r) is not
> callable using argument types (Result)
>
>      points.linearRemove(takeOne(find!(p => p.x > 7)(points[])));
>      // test.d(21): Error: template
> std.container.DList!(Point).DList.linearRemove cannot deduce
> function from argument types !()(Result), candidates are:
>      // /usr/include/dmd/phobos/std/container.d(2234):
> std.container.DList!(Point).DList.linearRemove(R)(R r) if (is(R
> == Range))
>      // /usr/include/dmd/phobos/std/container.d(2240):
> std.container.DList!(Point).DList.linearRemove(R)(R r) if (is(R
> == Range))
>      // /usr/include/dmd/phobos/std/container.d(2253):
> std.container.DList!(Point).DList.linearRemove(R)(R r) if (is(R
> == Take!Range))
>
>      points.remove(find!(p => p.x > 7)(points[]));
>      // 0
>
>      points.remove(takeOne(filter!(p => p.x > 7)(points[])));
>      // test.d(30): Error: function
> std.container.DList!(Point).DList.remove (Range r) is not
> callable using argument types (Result)
>
>      points.remove(filter!(p => p.x > 7)(points[]));
>      // test.d(33): Error: function
> std.container.DList!(Point).DList.remove (Range r) is not
> callable using argument types (FilterResult!(__lambda3, Range))
>
>      points.linearRemove(filter!(p => p.x > 7)(points[]));
>      // test.d(36): Error: template
> std.container.DList!(Point).DList.linearRemove cannot deduce
> function from argument types !()(FilterResult!(__lambda1,
> Range)), candidates are:
>      // /usr/include/dmd/phobos/std/container.d(2234):
> std.container.DList!(Point).DList.linearRemove(R)(R r) if (is(R
> == Range))
>      // /usr/include/dmd/phobos/std/container.d(2240):
> std.container.DList!(Point).DList.linearRemove(R)(R r) if (is(R
> == Range))
>      // /usr/include/dmd/phobos/std/container.d(2253):
> std.container.DList!(Point).DList.linearRemove(R)(R r) if (is(R
> == Take!Range))
>
>      foreach (Point p; points) {
>          if (p.x > 7) {
>              //points.remove(/* Somehow get the range */);
>              break;
>          }
>      }
>
>      foreach (Point p; points) {
>          writeln(p.x);
>      }
> }
>
>
> Purpose is to remove one element that matches predicate, or any
> amount really. Now DList.remove is defined as "Range remove(Range
> r)" and filter is "auto filter(Range)(Range rs) if
> (isInputRange!(Unqual!Range))" with explanation "The call
> filter!(predicate)(range) returns a new range only containing
> elements x in range for which predicate(x) is true." So if I
> understand correctly, filter should return a range that I can
> remove from the list. Why isn't this working?

std.container isn't great and hasn't received enough attention. There are plans to improve it, but I believe we're waiting on std.allocator and possibly a higher level layer on top of it before any significant revamp is made. It is perfectly usable in its current state however, just not always totally pleasant.
Don't let this put you off std.algorithm and std.range, which are both very high quality.

On Sunday, 9 March 2014 at 09:06:51 UTC, John Colvin wrote:
> std.container isn't great and hasn't received enough attention. There are plans to improve it, but I believe we're waiting on std.allocator and possibly a higher level layer on top of it before any significant revamp is made. It is perfectly usable in its current state however, just not always totally pleasant.
> Don't let this put you off std.algorithm and std.range, which are both very high quality.

Actually, DList is very hard to use.