• Tim K. (48/48) Dec 09 2015 Hi!
• BBaz (35/41) Dec 09 2015 You should read the documentation, there is two errors:
• Tim K. (6/8) Dec 09 2015 I guess I did read it wrong. Sorry.
• Andrea Fontana (11/19) Dec 09 2015 void main(string[] argv)
• cym13 (20/24) Dec 09 2015 Here are some elements of strategy:
• Andrea Fontana (9/13) Dec 09 2015 Maybe something like this works better:

Tim K. <no nope.com> writes:

Hi!

I'm trying to remove an item from an array of objects. But I get 
error messages when compiling (see below) which I do not 
understand. I figured I had to override opEquals for it to work, 
but no.
How do I get this to work?

Regards



     class A
     {
         this(string si, uint ui) { s = si; u = ui; }
         string s;
         uint u;

         override bool opEquals(Object obj)
         {
             A o = cast(A)obj;
             return (s == o.s) && (u == o.u);
         }
     }

     int main(string[] argv)
     {
         import std.stdio: writeln;
         import std.algorithm: remove;
         A a = new A("a", 1);
         A b = new A("b", 2);
         A[] as = [a, b];
         as.remove(a);
         writeln(as);

         return 0;
     }


Error:

/usr/include/dmd/phobos/std/algorithm/mutation.d(1503): Error: 
template std.range.primitives.popFrontExactly cannot deduce 
function from argument types !()(A[], A), candidates are:
/usr/include/dmd/phobos/std/range/primitives.d(1791):        
std.range.primitives.popFrontExactly(Range)(ref Range r, size_t 
n) if (isInputRange!Range)
/usr/include/dmd/phobos/std/algorithm/mutation.d(1504): Error: 
template std.range.primitives.popFrontExactly cannot deduce 
function from argument types !()(A[], A), candidates are:
/usr/include/dmd/phobos/std/range/primitives.d(1791):        
std.range.primitives.popFrontExactly(Range)(ref Range r, size_t 
n) if (isInputRange!Range)
/usr/include/dmd/phobos/std/algorithm/mutation.d(1505): Error: 
cannot implicitly convert expression (from) of type dummy.A to 
ulong
dummy.d(21): Error: template instance 
std.algorithm.mutation.remove!(cast(SwapStrategy)2, A[], A) error 
instantiating

BBaz <b2.temp gmx.com> writes:

On Wednesday, 9 December 2015 at 13:05:31 UTC, Tim K. wrote:
 Hi!

 I'm trying to remove an item from an array of objects. But I 
 get error messages when compiling (see below) which I do not 
 understand. I figured I had to override opEquals for it to 
 work, but no.
 How do I get this to work?

You should read the documentation, there is two errors:

1) remove works with an index
2) remove does not remove in place

so with

~~~~~~~~~~~~~~~~~~~~~~~~~~
import std.stdio;
import std.algorithm;

class A
{
     this(string si, uint ui) { s = si; u = ui; }
     string s;
     uint u;

     override bool opEquals(Object obj) const
     {
         if (A o = cast(A)obj)
             return (s == o.s) && (u == o.u);
         else
             return false;
     }
}

void main(string[] argv)
{
     A a = new A("a", 1);
     A b = new A("b", 2);
     A[] as = [a, b];
     as = as.remove(0);
     writeln(as);
}
~~~~~~~~~~~~~~~~~~~~~~~~~~

also, off topic but 2 other advices/errors

3) opEquals can be 'const' because the method doesn't mutate the 
state of the object
4) your cast wasn't safe

Tim K. <no nope.com> writes:

On Wednesday, 9 December 2015 at 13:13:36 UTC, BBaz wrote:

 1) remove works with an index

I guess I did read it wrong. Sorry.
Is there a convenience function that allows me to remove an/all 
object(s) with a certain value from an array or do I need to 
write one myself?

 2) remove does not remove in place

That's fine.

Andrea Fontana <nospam example.com> writes:

On Wednesday, 9 December 2015 at 13:23:00 UTC, Tim K. wrote:
 On Wednesday, 9 December 2015 at 13:13:36 UTC, BBaz wrote:

 1) remove works with an index

 I guess I did read it wrong. Sorry.
 Is there a convenience function that allows me to remove an/all 
 object(s) with a certain value from an array or do I need to 
 write one myself?

 2) remove does not remove in place

 That's fine.

void main(string[] argv)
{
     A a = new A("a", 1);
     A b = new A("b", 2);
     A[] as = [a, b];
     as = as.remove!(x => x == a);
     writeln(as);
}

If array is sorted you can find the index of that element and 
then remove it by index.

cym13 <cpicard openmailbox.org> writes:

On Wednesday, 9 December 2015 at 13:23:00 UTC, Tim K. wrote:
 On Wednesday, 9 December 2015 at 13:13:36 UTC, BBaz wrote:

 Is there a convenience function that allows me to remove an/all 
 object(s) with a certain value from an array or do I need to 
 write one myself?

Here are some elements of strategy:

      import std.algorithm;
      import std.array;

      auto arr = [2, 3, 4, 5, 3, 2, 4];

      // Remove all
      arr = arr.remove!(x => x==3);
      assert(arr == [2, 4, 5, 2, 4];);

      // remove all (filter works lazilly, we use array to get an 
array nonetheless)
      // filter is useful when composing functions, not so much 
here
      arr = arr.filter!(x => x==2).array;
      assert(arr == [4, 5, 4]);

      // Remove one, throw if the element is not found,
      // we use countUntil to get the index.
      arr = arr.remove(arr.countUntil(4));
      assert(arr == [5, 4]);

also you may be interested in reading this:

http://p0nce.github.io/d-idioms/#Adding-or-removing-an-element-from-arrays

Andrea Fontana <nospam example.com> writes:

On Wednesday, 9 December 2015 at 13:13:36 UTC, BBaz wrote:
 3) opEquals can be 'const' because the method doesn't mutate 
 the state of the object
 4) your cast wasn't safe




Maybe something like this works better:

...

     override bool opEquals(T)(T obj) const
     if (is(T : A))
     {
         return (s == o.s) && (u == o.u);
     }

...