Seed Value for reduce function

[Ali Çehreli]

On 12/09/2017 06:19 PM, Vino wrote:

>   Tried with fold even then it is failing same as reduce with the same 
> error when there is empty folder
> 
> auto SdFiles = Array!ulong(dirEntries(d, SpanMode.depth).map!(a => 
> a.size).fold!((a,b) => a + b))[].filter!(a => a  > Size);

When no seed value is specified, fold (and reduce) take the first 
element as the seed. When the range is empty, then there is a run-time 
failure:

object.Exception@/usr/include/dmd/phobos/std/algorithm/iteration.d(2794): 
Cannot reduce an empty input range w/o an explicit seed value.

The solution is to provide an explicit seed value:

import std.container;
import std.file;
import std.algorithm;

void main() {
     const d = "/tmp/empty_folder";
     const Size = 42;
     auto SdFiles = Array!ulong(dirEntries(d, SpanMode.depth).map!(a => 
a.size).fold!((a,b) => a + b)(size_t(0)))[].filter!(a => a  > Size);
}

I chose size_t(0) but you can use a variable, size_t.init, etc.

Ali