generate with state

[Ali Çehreli via Digitalmars-d-learn]

On 11/02/2015 03:56 PM, Freddy wrote:
> Is there a version of http://dlang.org/phobos/std_range.html#.generate
> with state.

generate() already allows "callables", which can be a delegate:

import std.stdio;
import std.range;

struct S {
     int i;

     int fun() {
         return i++;
     }
}

void main() {
     auto s = S(42);
     writefln("%(%s %)", generate(&s.fun).take(5));
}

Prints

42 43 44 45 46

Shorter but more cryptic:

   ... generate(&S(42).fun).take(5)

If the generation process is naturally recursive like traversing a tree, 
then you may want to consider std.concurrency.Generator (which does not 
involve multiple threads at all):

   http://dlang.org/phobos/std_concurrency.html#.Generator

Here is an example:

 
http://ddili.org/ders/d.en/fibers.html#ix_fibers.Generator,%20std.concurrency

import std.stdio;
import std.range;
import std.concurrency;

/* This alias is used for resolving the name conflict with
  * std.range.Generator. */
alias FiberRange = std.concurrency.Generator;

void fibonacciSeries() {
     int current = 0;
     int next = 1;

     while (true) {
         yield(current);

         const nextNext = current + next;
         current = next;
         next = nextNext;
     }
}

void main() {
     auto series = new FiberRange!int(&fibonacciSeries);
     writefln("%(%s %)", series.take(10));
}

Ali