Problem with C++ ranges also exhibited by D

[Atila Neves]

This blog post shows off some problems with the ranges v3 library 
that is going to be included in the C++20 standard library:

https://www.fluentcpp.com/2019/04/16/an-alternative-design-to-iterators-and-ranges-using-stdoptional/

Because the problem is basically (from the blog) "Is it really 
necessary to have separate operations for advancing the iterator 
and evaluating its element?". The answer is of course no, and 
this has been brought up in the forums before. Like it or not, D 
has the same issue:

-----------------------------
import std.algorithm;
import std.range;
import std.stdio;

void main() {
     iota(1, 6)
         .map!((n) { writeln("transform ", n); return n * 2; })
         .filter!(n => n % 4 == 0)
         .writeln;
}
-----------------------------

Produces the output:

[transform 1
transform 2
transform 2
4transform 3
transform 4
, transform 4
8transform 5
]

Showing that the mapped function is called more times than 
strictly necessary, just as in C++.