Behavior of joining mapresults

[Jonathan M Davis]

On Thursday, December 21, 2017 07:46:03 Christian Köstlin via Digitalmars-d-
learn wrote:
> On 20.12.17 17:30, Christian Köstlin wrote:
> > thats an idea, thank a lot, will give it a try ...
>
> #!/usr/bin/env rdmd -unittest
> unittest {
>     import std.stdio;
>     import std.range;
>     import std.algorithm;
>     import std.string;
>     import std.functional;
>
>     auto parse(int i) {
>         writeln("parsing %s".format(i));
>         return [1, 2, 3];
>     }
>
>     writeln(iota(1, 5).map!(memoize!parse));
>     writeln("-------------------------------");
>     writeln((iota(1, 5).map!(memoize!parse)).joiner);
> }
>
> void main() {}
>
> works, but i fear for the data that is stored in the memoization. at the
> moment its not a big issue, as all the data fits comfortable into ram,
> but for bigger data another approach is needed (probably even my current
> json parsing must be exchanged).
>
> I still wonder, if the joiner calls front more often than necessary. For
> sure its valid to call front as many times as one sees fit, but with a
> lazy map in between, it might not be the best solution.

I would think that it would make a lot more sense to simply put the whole
thing in an array than to use memoize. e.g.

auto arr = iota(1, 5).map!parse().array();

- Jonathan M Davis