• Antonio (25/25) Jun 10 2022 When mapping and filtering, the last mapped element is evaluated
• Steven Schveighoffer (19/47) Jun 10 2022 `map` calls the lambda for each call to `front`. If you want a cached
• =?UTF-8?Q?Ali_=c3=87ehreli?= (7/9) Jun 10 2022 Others don't know but as I will likely show during a lightning talk at
• Salih Dincer (4/8) Jun 16 2022 I guess the developed cached() and cache() are different things,
• =?UTF-8?Q?Ali_=c3=87ehreli?= (8/11) Jun 16 2022 cache caches only the front element.
• Antonio (3/7) Jun 12 2022 Thank you very much, Steve

Antonio <antonio abrevia.net> writes:

When mapping and filtering, the last mapped element is evaluated 
twice... Is it the expected behaviour?

```d
void main()
{
     import std.algorithm, std.stdio;
	
     [1,2,3,4,5].
		map!((x){
         	writeln("mapping ", x);
         	return x;
     	}).
		filter!(x=>x>2).
		front.
		writeln();
}
```

Output
```
mapping 1
mapping 2
mapping 3
mapping 3
3

```

Steven Schveighoffer <schveiguy gmail.com> writes:

On 6/10/22 4:33 PM, Antonio wrote:
 When mapping and filtering, the last mapped element is evaluated 
 twice... Is it the expected behaviour?
 
 ```d
 void main()
 {
      import std.algorithm, std.stdio;
 
      [1,2,3,4,5].
          map!((x){
              writeln("mapping ", x);
              return x;
          }).
          filter!(x=>x>2).
          front.
          writeln();
 }
 ```
 
 Output
 ```
 mapping 1
 mapping 2
 mapping 3
 mapping 3
 3
 
 ```

`map` calls the lambda for each call to `front`. If you want a cached 
version, use `cache`:

```d
void main()
{
     import std.algorithm, std.stdio;

     [1,2,3,4,5].
         map!((x){
             writeln("mapping ", x);
             return x;
         }).
         cache.
         filter!(x=>x>2).
         front.
         writeln();
}
```

-Steve

=?UTF-8?Q?Ali_=c3=87ehreli?= <acehreli yahoo.com> writes:

On 6/10/22 13:47, Steven Schveighoffer wrote:

 `map` calls the lambda for each call to `front`. If you want a cached
 version, use `cache`:

Others don't know but as I will likely show during a lightning talk at 
DConf, I am trying to finish a .cached range algorithm that caches all 
elements that are in use. (It must drop old elements so that an infinite 
range does not require infinite cache.)

It is supposed to evaluate elements only once.

Ali

Salih Dincer <salihdb hotmail.com> writes:

On Friday, 10 June 2022 at 22:10:10 UTC, Ali Çehreli wrote:
 [...] I am trying to finish a .cached range algorithm that 
 caches all elements that are in use. (It must drop old elements 
 so that an infinite range does not require infinite cache.)

 It is supposed to evaluate elements only once.

I guess the developed cached() and cache() are different things, 
right? I tried cached(), it works fine and cleverly designed...

SDB 79

=?UTF-8?Q?Ali_=c3=87ehreli?= <acehreli yahoo.com> writes:

On 6/16/22 00:58, Salih Dincer wrote:

 I guess the developed cached() and cache() are different things,
 right?

cache caches only the front element.

   https://dlang.org/library/std/algorithm/iteration/cache.html

 I tried cached()

cached() is supposed to cache as many elements as needed as long as 
there are ranges that still reference the elements. Technically, 
cached() does not exist because only a couple of people have seen a 
draft of it. :)

Ali

Antonio <antonio abrevia.net> writes:

On Friday, 10 June 2022 at 20:47:14 UTC, Steven Schveighoffer 
wrote:
 On 6/10/22 4:33 PM, Antonio wrote:
 ...

 `map` calls the lambda for each call to `front`. If you want a 
 cached version, use `cache`:

Thank you very much, Steve