A little help with Ranges

[Steven Schveighoffer]

On 8/27/21 12:41 AM, Merlin Diavova wrote:
> On Friday, 27 August 2021 at 04:01:19 UTC, Ali Çehreli wrote:
>> On 8/26/21 7:17 PM, Merlin Diavova wrote:
>>
>>> [...]
>>
>> Then the operations downstream will not produce any results. For 
>> example, the array will be empty below:
>>
>> import std.stdio;
>> import std.range;
>> import std.algorithm;
>> import std.string;
>> import std.functional;
>>
>> void main() {
>>   auto significantLines = stdin
>>                           .byLineCopy
>>                           .map!strip
>>                           .filter!(not!empty)
>>                           .filter!(line => line.front != '#')
>>                           .array;
>>
>>   if (significantLines.empty) {
>>     writeln("There were no significant lines.");
>>
>>   } else {
>>     writefln!"The lines: %-(\n%s%)"(significantLines);
>>   }
>> }
>>
>> Ali
> 
> And there it is!
> 
> I was missing
> 
> ```d
> .filter!(not!empty)
> ```
> 
> My code now works exactly how I wanted. Thanks!

Be careful with this! `not!empty` is *only* working because you are 
using arrays (where `empty` is a UFCS function defined in std.range). 
Other ranges this will not work on. Instead, I would recommend a lambda 
(which will work with arrays too):

```d
.filter!(r => !r.empty)
```

-Steve