Ruby-style "each" in D?

[bearophile]

Andrei Alexandrescu:

> Pros and cons are already being discussed. Destroy!
>
> https://github.com/D-Programming-Language/phobos/pull/2024

I proposed the same function in D.learn, but this discussion 
needs a list of use cases and usage examples, otherwise you can't 
decide in vacuum.

It's named "foreach" in Scala:
http://twitter.github.io/scala_school/collections.html#foreach

Elsewhere I suggested a function that could be named tap() that's 
usable to debug UFCS chains, interspersing it in the chain, to 
add imperative calls to writeln. You can replace a each() with a 
tap + some kind of eager consumer.

In many cases what I want to put in each() is a writef/writefln, 
you can do it like this (binaryReverseArgs is in std.functional):

foo
.bar
.spam
.binaryReverseArgs!writefln("%(%s-%): %d", 5);

With a shorter flipping name it gets better:

foo
.bar
.spam
.flipTwoArgs!writefln("%(%s-%): %d", 5);

or even (http://zvon.org/other/haskell/Outputprelude/flip_f.html 
) (flips only the first two args and doesn't flip the successive 
ones):

foo
.bar
.spam
.flip!writefln("%(%s-%): %d", 5);

Let's say in each() you want to do something different, like 
incrementing a variable:

foo
.bar
.spam
.each!(n => x += n);

Is this good enough?

If you want to double the contents of an array:

myArray.each((ref x) => x * 2);

But in D you can also use:

myArray[] *= 2;

I guess you can't use each() on opApply-based iterables, while 
you can with foreach(). This makes each() less useful.

Is the following code supported? And what is each() receiving 
from the associative array?

int[string] aa;
aa.each(...);

Perhaps you must use:

int[string] aa;
aa.byKey.each(...);
aa.byValue.each(...);
aa.byPair.each(...);

While arrays should be OK, but there is no index support:

int[] arr;
arr.each(...);

If you need dynamic array index support:

int[] arr;
arr.enumerate.each(...);

Is this supported?

int[10] arr2;
arr2.each(...);

Or do you have to use this?

int[10] arr2;
arr2[].each(...);

Bye,
bearophile