## digitalmars.D.learn - New to std.algorithm and generics, no idea how to make simple things

• newguy (78/78) Mar 07 2014 I really can't wrap my head around these. I fought whole day
• newguy (2/2) Mar 07 2014 Text went nuts at least for me so here's raw pastebin of it
• newguy (7/7) Mar 08 2014 Ok, I got it working with
• bearophile (6/8) Mar 08 2014 It is complicated. Other parts of Phobos are both less complex
• John Colvin (8/89) Mar 09 2014 std.container isn't great and hasn't received enough attention.
• monarch_dodra (2/9) Mar 11 2014 Actually, DList is very hard to use.
```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?
```
Mar 07 2014
```Text went nuts at least for me so here's raw pastebin of it
http://pastebin.com/raw.php?i=JfLFdsNj
```
Mar 07 2014
```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 :)
```
Mar 08 2014
"bearophile" <bearophileHUGS lycos.com> writes:
```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
```
Mar 08 2014
"John Colvin" <john.loughran.colvin gmail.com> writes:
```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.
```
Mar 09 2014
"monarch_dodra" <monarchdodra gmail.com> writes:
```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.
```
Mar 11 2014