# [Issue 5466] New: AA ranges

`http://d.puremagic.com/issues/show_bug.cgi?id=5466`
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Summary: AA ranges
Product: D
Version: D2
Platform: All
OS/Version: All
Status: NEW
Severity: enhancement
Priority: P2
Component: druntime
AssignedTo: s...@invisibleduck.org
ReportedBy: bearophile_h...@eml.cc

--- Comment #0 from bearophile_h...@eml.cc 2011-01-20 04:06:22 PST ---
I use D associative arrays often so I'd like AAs to be modified so byKey() and
byValue() return ranges (that have a length attribute too) usable with higher
order functions of std.algorithm like map and filter.

AAs too may become iterable with no method calls:
map!q{a * 10}([1:2, 3:4])

I also suggest to add a third associative array member function that returns a
range of (key,value) typecons tuples, as in a similar Python3 dict method.

------------------

To test the situation, this task is to create a dynamic array of pairs (tuples)
like:
[(10,"aa"), (20,"bb"), (30,"cc")]

from the associative array:
[1:'a', 2:'b', 3:'c']

If possible reading things lazily from the associative array.

Idiomatic Python2 solution (iteritems is lazy):

>>> d = {1:'a', 2:'b', 3:'c'}
>>> [(k*10, v*2) for k,v in d.iteritems()]
[(10, 'aa'), (20, 'bb'), (30, 'cc')]

D2 lazy solution without map():

import std.stdio, std.typecons;
void main() {
auto aa = [1:'a', 2:'b', 3:'c'];
Tuple!(int, string)[] r;
foreach (k, v; aa)
r ~= tuple(k*10, ""~v~v);
writeln(r);
}

The byPair() range allows to solve the task functionally ad lazily like this:

import std.stdio, std.typecons, std.algorithm;
void main() {
auto aa = [1:'a', 2:'b', 3:'c'];
auto r = map!q{ tuple(a[0]*10, a[1]~a[1]) }(aa.byPair());
writeln(r);
}

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