Ultra-pure map()?

[FreeSlave]

On Saturday, 28 December 2013 at 09:18:00 UTC, David Held wrote:
> On 12/27/2013 7:32 PM, Marco Leise wrote:> [...]
> > Side effects and altering the input object itself makes me
> > want to pull out my crucifix. You shall not have impurity in
> > your functional style code!
>
> Why not?  There are many impure functional languages, and most 
> non-functional languages that allow functional style allow 
> mutation. OOP is all about hiding state, which is the opposite 
> of referential transparency.  Are you saying we should never 
> map/fold over OOP ranges?
>  That seems like an unnecessary restriction for dogma's sake. 
> Obviously, map() has to be lazy to support infinite ranges.  
> But I assume that reduce() must be eager so that you actually 
> get a result (I mean, it could probably be made lazy at 
> enormous expense, but that would just be silly).  So, if you 
> want side effects, I guess you have to do the slightly dirty 
> trick of calling reduce() without actually reducing anything.
>
> I guess the "right" thing to do would be to make a new 
> algorithm that implements an eager map() but perhaps doesn't 
> bother with the result, called "invoke()".  This carries none 
> of the semantic baggage of well-known pure higher-order 
> functions, and even sounds more OOP-like. Most of the other 
> features of map() (like parallel iteration) are pretty nice to 
> have in eager form.
>
> Dave

If you want to get result just now, then use 'array' function 
from std.array module.

map!fun(range).array;

or

array(map!fun(range));