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digitalmars.D.learn - How do I make my class iterable?

reply "Assembly" <jckj33 gmail.com> writes:

(https://msdn.microsoft.com/en-us/library/65zzykke.aspx)? if so, 
where can I find it?

What I want is loop over a user-defined class/struct. In case of 

methods that's called by the foreach() construct together with 
the yield keyword I "feed" the loop until the moveNext() returns 

example.

  Something like this:

struct MyStruct
{
    // proper methods/proeperties called by foreach() to iterate
    // over the array
    int[] myarr;
    int = 0;
    int getNext() { return myarr[i]; }
    bool hasNext() { return i == myarr.length; }
}

MyStruct s;
foreach(MyStruct x; s)
{

}

Is this possible?
Jun 22 2015
parent reply "q66" <daniel octaforge.org> writes:
On Monday, 22 June 2015 at 16:33:43 UTC, Assembly wrote:


 (https://msdn.microsoft.com/en-us/library/65zzykke.aspx)? if 
 so, where can I find it?

 What I want is loop over a user-defined class/struct. In case 

 methods that's called by the foreach() construct together with 
 the yield keyword I "feed" the loop until the moveNext() 
 returns false (no next element). The think I've linked has some 


  Something like this:

 struct MyStruct
 {
    // proper methods/proeperties called by foreach() to iterate
    // over the array
    int[] myarr;
    int = 0;
    int getNext() { return myarr[i]; }
    bool hasNext() { return i == myarr.length; }
 }

 MyStruct s;
 foreach(MyStruct x; s)
 {

 }

 Is this possible?


use opApply.
Jun 22 2015
parent reply =?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:
On 06/22/2015 09:37 AM, q66 wrote:


 use opApply.


Yes. Additionally, an InputRange interface can be used:

   http://ddili.org/ders/d.en/foreach_opapply.html

Ali
Jun 22 2015
parent reply "Assembly" <jckj33 gmail.com> writes:
On Monday, 22 June 2015 at 16:52:15 UTC, Ali Çehreli wrote:

 On 06/22/2015 09:37 AM, q66 wrote:


 use opApply.


 Yes. Additionally, an InputRange interface can be used:

   http://ddili.org/ders/d.en/foreach_opapply.html

 Ali


I was reading exaclty this page that.

I've had implmented this method/properties (I remembered how 
foreach() is translated to for() by the compiler using 
front/popFront() and such):

T front() { return _app.data[index]; }
T front(int index, T a) { return _app.data[index]; }


	void popFront()
	{
		index++;
	}


and called like this:

foreach(int i, MyType p; places) {

but I get this error:

Error: cannot infer argument types, expected 1 argument, not 2

to try solve that error I added the overload method:

T front(int index, T a)

but it didn't worked. How do I solve this?
Jun 22 2015
next sibling parent reply Steven Schveighoffer <schveiguy yahoo.com> writes:
On 6/22/15 1:03 PM, Assembly wrote:

 On Monday, 22 June 2015 at 16:52:15 UTC, Ali Çehreli wrote:

 On 06/22/2015 09:37 AM, q66 wrote:


 use opApply.


 Yes. Additionally, an InputRange interface can be used:

   http://ddili.org/ders/d.en/foreach_opapply.html

 Ali


 I was reading exaclty this page that.

 I've had implmented this method/properties (I remembered how foreach()
 is translated to for() by the compiler using front/popFront() and such):

 T front() { return _app.data[index]; }
 T front(int index, T a) { return _app.data[index]; }


      void popFront()
      {
          index++;
      }


 and called like this:

 foreach(int i, MyType p; places) {

 but I get this error:

 Error: cannot infer argument types, expected 1 argument, not 2

 to try solve that error I added the overload method:

 T front(int index, T a)

 but it didn't worked. How do I solve this?


TBH, opApply is much better suited to classes.

But in order to have multiple parameters with foreach by using a range, 
you must return a tuple:

auto front() { import std.typecons: tuple; return tuple(index, 
_app.data[index]);}

Note, do NOT do this on your class, you should be creating a range 
struct type, and return the range from opIndex() with no parameters.

-Steve
Jun 22 2015
parent reply "Assembly" <jckj33 gmail.com> writes:
On Monday, 22 June 2015 at 17:09:16 UTC, Steven Schveighoffer 
wrote:

 On 6/22/15 1:03 PM, Assembly wrote:

 [...]


 TBH, opApply is much better suited to classes.

 But in order to have multiple parameters with foreach by using 
 a range, you must return a tuple:

 auto front() { import std.typecons: tuple; return tuple(index, 
 _app.data[index]);}

 Note, do NOT do this on your class, you should be creating a 
 range struct type, and return the range from opIndex() with no 
 parameters.

 -Steve


I'm using this, thanks for all. Can someone clarify how does 
opApply() works? I assume it's called every iteration and as 
opApply() has a loop does it means the number of iteration ran 
actually is the ones from foreach() is 2*n where n is the number 
of elements in the array, is this right?
Jun 22 2015
parent reply "anonymous" <anonymous example.com> writes:
On Monday, 22 June 2015 at 18:44:22 UTC, Assembly wrote:

 I'm using this, thanks for all. Can someone clarify how does 
 opApply() works? I assume it's called every iteration and as 
 opApply() has a loop does it means the number of iteration ran 
 actually is the ones from foreach() is 2*n where n is the 
 number of elements in the array, is this right?


opApply is called only once. The body of the foreach is passed to 
opApply as a delegate. The opApply implementation runs the 
supplied foreach body, possibly in a loop. Every such call is an 
iteration of the foreach loop.

With opApply this:
     foreach(x; iterable) {/* do something with x */}
gets rewritten to this:
     iterable.opApply((x) {/* do something with x */});
Jun 22 2015
parent "Assembly" <jckj33 gmail.com> writes:
On Monday, 22 June 2015 at 20:34:00 UTC, anonymous wrote:

 On Monday, 22 June 2015 at 18:44:22 UTC, Assembly wrote:

 I'm using this, thanks for all. Can someone clarify how does 
 opApply() works? I assume it's called every iteration and as 
 opApply() has a loop does it means the number of iteration ran 
 actually is the ones from foreach() is 2*n where n is the 
 number of elements in the array, is this right?


 opApply is called only once. The body of the foreach is passed 
 to opApply as a delegate. The opApply implementation runs the 
 supplied foreach body, possibly in a loop. Every such call is 
 an iteration of the foreach loop.

 With opApply this:
     foreach(x; iterable) {/* do something with x */}
 gets rewritten to this:
     iterable.opApply((x) {/* do something with x */});


got it, thanks :)
Jun 22 2015
prev sibling parent reply =?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:
On 06/22/2015 10:03 AM, Assembly wrote:


 foreach(int i, MyType p; places) {

 but I get this error:

 Error: cannot infer argument types, expected 1 argument, not 2


Yeah, the loop counter is automatic only for slices. You can use 
'enumerate' for other types:

     foreach (i, element; NumberRange(42, 47).enumerate) {
         // ...
     }

That is taken from the same page: ;)

 
http://ddili.org/ders/d.en/foreach_opapply.html#ix_foreach_opapply.loop%20counter

Ali
Jun 22 2015
parent reply "Assembly" <jckj33 gmail.com> writes:
On Monday, 22 June 2015 at 18:07:36 UTC, Ali Çehreli wrote:

 On 06/22/2015 10:03 AM, Assembly wrote:


 foreach(int i, MyType p; places) {

 but I get this error:

 Error: cannot infer argument types, expected 1 argument, not 2


 Yeah, the loop counter is automatic only for slices. You can 
 use 'enumerate' for other types:

     foreach (i, element; NumberRange(42, 47).enumerate) {
         // ...
     }

 That is taken from the same page: ;)


 http://ddili.org/ders/d.en/foreach_opapply.html#ix_foreach_opapply.loop%20counter

 Ali


if my opApply() is defiend as the following:

int opApply(int delegate(ref int, ref T) del)
	{
		int result;

		foreach(int i, T val; _app.data)
		{
			result = del(i, _app.data[i]);
			
			if(result)
				break;
		}

		return result;
	}

and called like:

foreach(int i, MyType p; places) {

isn't i the loop counter?
Jun 22 2015
parent =?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:
On 06/22/2015 11:48 AM, Assembly wrote:


 if my opApply() is defiend as the following:

 int opApply(int delegate(ref int, ref T) del)
      {


[...]

      }

 and called like:

 foreach(int i, MyType p; places) {

 isn't i the loop counter?


size_t is more natural but yes, that's it.

Ali
Jun 22 2015