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[Issue 9611] New: std.algorithm.nWayUnion(Tuple) too?
Feb 28, 2013
Chris Cain
```http://d.puremagic.com/issues/show_bug.cgi?id=9611

Summary: std.algorithm.nWayUnion(Tuple) too?
Product: D
Version: D2
Platform: All
OS/Version: All
Status: NEW
Severity: enhancement
Priority: P2
Component: Phobos
AssignedTo: nobody@puremagic.com
ReportedBy: bearophile_hugs@eml.cc

--- Comment #0 from bearophile_hugs@eml.cc 2013-02-27 15:12:43 PST ---
In some cases I have had to merge ranges of different type. So maybe for such situations it's worth supporting nWayUnion of a Tuple of ranges:

import std.algorithm: nWayUnion, map;
import std.range: iota;
import std.typecons: tuple;
void main() {
auto a = iota(10);
auto b = [3, 6, 9];
auto c = iota(11).map!q{a * a};
auto r = nWayUnion(tuple(a, b, c));
}

Note: in all such of my usage cases the number of the ranges was limited, 2 or 3. So when the input of nWayUnion is a tuple I think there is no need for nWayUnion to keep the ranges inside with a BinaryHeap.

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

Current workaround, suggested by Ali Çehreli:

import std.algorithm: nWayUnion, map;
import std.range: iota, InputRange, inputRangeObject;
void main() {
InputRange!int a = inputRangeObject(iota(10));
InputRange!int b = inputRangeObject([3, 6, 9]);
InputRange!int c = inputRangeObject(iota(11).map!q{a * a});
auto r = nWayUnion([a, b, c]);
}

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Chris Cain <zshazz@gmail.com> changed:

----------------------------------------------------------------------------
CC|                            |zshazz@gmail.com

--- Comment #1 from Chris Cain <zshazz@gmail.com> 2013-02-27 17:13:37 PST ---
> Current workaround, suggested by Ali Çehreli:
>
> import std.algorithm: nWayUnion, map;
> import std.range: iota, InputRange, inputRangeObject;
> void main() {
>     InputRange!int a = inputRangeObject(iota(10));
>     InputRange!int b = inputRangeObject([3, 6, 9]);
>     InputRange!int c = inputRangeObject(iota(11).map!q{a * a});
>     auto r = nWayUnion([a, b, c]);
> }

A function that does the conversion to InputRange!E could easily be created and added to Phobos to handle this type of situation. Ranges such as nWayUnion could call this (currently poorly named) tupWrapper when isTuple!T returns true.

---

import std.stdio, std.range, std.typecons, std.algorithm;

void main() {
auto tup = tuple(iota(5), repeat(1).take(3), [5,9,30]);

foreach(e; tupWrapper(tup).nWayUnion())
writeln(e);
}

auto tupWrapper(Tup)(Tup tup) {
alias E = ElementType!(Tup.Types[0]);
InputRange!E[] arr;
foreach(T; Tup.Types)
static assert(is(ElementType!T == E));

foreach(ref e; tup)
arr ~= inputRangeObject(e);

return arr;
}

---

Currently, that solution isn't too robust. Ideally it would figure out the most powerful range type (either InputRange, ForwardRange, ..., RandomAccessRange) that all the types in the Tuple.Types support and it would return that.

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--- Comment #2 from bearophile_hugs@eml.cc 2013-02-27 17:24:55 PST ---

> A function that does the conversion to InputRange!E could easily be created and added to Phobos to handle this type of situation.

I think InputRange and inputRangeObject are not needed to solve this. A "static foreach" on the Tuple fields (that contain ranges) looking for the smallest value seems enough to me.

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Andrei Alexandrescu <andrei@erdani.com> changed: