Re: Using algorithms with ranges

[mipri via Digitalmars-d-learn]

On Thursday, 3 October 2019 at 05:20:47 UTC, mipri wrote:

It'd be nicer to do compose a range over iota, as in

  iota(1, 10).newThingWithHistory

but I don't know how to do that yet. I guess c.f. std.range.retro

This is a bit better:

#! /usr/bin/env rdmd
import std.stdio;

auto withHistory(Range)(Range r) {
    import std.traits : Unqual;
    import std.range.primitives : ElementType;

    static struct Result {
    private:
        alias R = Unqual!Range;
        alias T = ElementType!R;

        R source;
        T[] history;

    public:
        bool empty() {
            return source.empty;
        }

        void popFront() {
            source.popFront;
        }

        T front() {
            T x = source.front;
            history ~= x;
            if (history.length > 1) {
                return x + history[$-2];
            } else {
                return x;
            }
        }
    }

    return Result(r);
}

void main() {
    import std.range : iota;

    foreach (x; iota(1, 10).withHistory)
        writeln(x);
}