Another task

[bearophile]

spir:

> Yes, this is the only nice looking, high-level, and D-style solution. 

I have added:
http://d.puremagic.com/issues/show_bug.cgi?id=5466


> While I by far prefer avoiding stringcode:
> 	auto r = map!((p) (tuple(p[0]*10, p[1]~p[1])) (aa.byPair());
> where p means pair; should be correct, should'nt it?

If you use a lambda template you need braces and the return statement:
auto r = map!((p){ return tuple(p[0]*10, p[1]~p[1]); })(aa.byPair());


> I think for a newcomer the most difficult part is related to tuples:
> * find them (in std.typecons!!!)
> * catch after much time, pains, research, they should not even try to 
> construct a tuple using Tuple!, but using the convenience tuple() func 
> instead.

I agree that like dynamic arrays, tuples are better as built-ins, in D too. Another very useful thing is tuple unpacking syntax:
http://d.puremagic.com/issues/show_bug.cgi?id=4579


> And also that map expects a range, which an AA is not according to my 
> trials (code rejected at link time until I used byKey). Or am I wrong?

You aren't wrong.

 
> PS: sh*t, I cannot have this work, what's wrong?
> 
> auto pairs = map!
>          ((int i) {return tuple(10*i, aa[i]~aa[i]);})
>          (aa.byKey());

Look at the answers by Simen kjaeraas in this thread, he has explained the situation.

Bye,
bearophile