Using closure causes GC allocation

[Nicholas Wilson via Digitalmars-d-learn]

On Monday, 4 September 2017 at 05:45:18 UTC, Vino.B wrote:
> On Saturday, 2 September 2017 at 20:54:03 UTC, Vino.B wrote:
>> On Saturday, 2 September 2017 at 20:10:58 UTC, Moritz Maxeiner 
>> wrote:
>>> On Saturday, 2 September 2017 at 18:59:30 UTC, Vino.B wrote:
>>>> [...]
>>>
>>> Cannot reproduce under Linux with dmd 2.076.0 (with commented 
>>> out Windows-only check). I'll try to see what happens on 
>>> Windows once I have a VM setup.
>>>
>>>> [...]
>>>
>>> You changed the type of dFiles, which you return from 
>>> cleanFiles, without changing the return type of cleanFiles. 
>>> Change the return type of cleanFiles to the type the compiler 
>>> error above tells you it should be (`Tuple!(string, 
>>> string)[]` instead of `string[][]`), or let the compiler 
>>> infer it via auto (`auto cleanFiles(...`).
>>
>> Hi,
>>
>>  Thank you very much, was able to resolve the second code 
>> issue by changing the return type of the function.
>
> Hi,
>
>   In order to resolve the issue "Using closure causes GC 
> allocation" it was stated that we need to use delegates, can 
> you please help me on how to as i have not gone that much far 
> in D programming.
>
> import std.stdio: File,writeln;
> import std.datetime.systime: Clock, days, SysTime;
> import std.file: SpanMode, dirEntries, exists, isFile, mkdir, 
> remove;
> import std.typecons: tuple, Tuple;
> import std.algorithm:  filter, map, each;
> import std.array: array;
>
> Tuple!(string)[] logClean (string[] Lglst, int LogAge) {
> 	if (!Lglst[0].exists) { mkdir(Lglst[0]); }
> 	auto ct1 = Clock.currTime();
> 	auto st1 = ct1 + days(-LogAge);
> 	auto dFiles = dirEntries(Lglst[0], SpanMode.shallow).filter!(a 
> => a.exists && a.isFile && a.timeCreated < st1).map!(a => 
> tuple(a.name)).array;
> 	dFiles.each!(a => a[0].remove);
> 	return dFiles;
> }
>
> void main () {
> string[] LogDir = 
> ["C:\\Users\\bheev1\\Desktop\\Current\\Script\\D\\Logs"];
> int  LogAge = 1;
> logClean(LogDir,LogAge);
> }
>
> From,
> Vino.B

If you are getting Using closure causes GC allocation from the 
above, it will be because you reference a local in the template 
delegate argument to filter:

filter!(a => a.exists &&
         a.isFile &&
         a.timeCreated < st1)
                        ^^^
because of the local (st1) it needs a closure. I can't remember 
how to transform delegates to take parameters and then call with 
the parameter set to the local, someone else will have to fill 
you in on that one.