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Fix Issue 9682 - group/filter should return a SortedRange when they are passed one #5712

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Fix Issue 9682 - group/filter should return a SortedRange when they are passed one #5712

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32 changes: 27 additions & 5 deletions std/algorithm/iteration.d
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Original file line number Diff line number Diff line change
Expand Up @@ -1093,7 +1093,8 @@ Params:

Returns:
$(D filter!(predicate)(range)) returns a new range containing only elements $(D x) in $(D range) for
which $(D predicate(x)) returns $(D true).
which $(D predicate(x)) returns $(D true). If a `SortedRange` is passed, the result is going to be
a `SortedRange`.

See_Also:
$(HTTP en.wikipedia.org/wiki/Filter_(higher-order_function), Filter (higher-order function))
Expand All @@ -1103,7 +1104,11 @@ if (is(typeof(unaryFun!predicate)))
{
auto filter(Range)(Range range) if (isInputRange!(Unqual!Range))
{
return FilterResult!(unaryFun!predicate, Range)(range);
import std.range : SortedRange, assumeSorted;
static if (is(Range : SortedRange!TT, TT))
return assumeSorted(FilterResult!(unaryFun!predicate, Range)(range));
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@andralex andralex Sep 1, 2017

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The sorting predicate should be propagated here, e.g. return FilterResult!(unaryFun!predicate, Range)(range).assumeSorted!TT;

else
return FilterResult!(unaryFun!predicate, Range)(range);
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@andralex andralex Sep 1, 2017

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Code is repetitive here, should be something like:

auto result = FilterResult!(unaryFun!predicate, Range)(range);
static if (is(Range : SortedRange!order, order))
    return result.assumeSorted!order;
else
    return result;

}
}

Expand Down Expand Up @@ -1259,6 +1264,11 @@ private struct FilterResult(alias pred, Range)
auto arr = [1,2,3,4,5];
auto m = map!"a + 1"(filter!"a < 4"(arr));
assert(equal(m, [2, 3, 4]));

// Issue 9682
import std.range : SortedRange, assumeSorted;
auto t = assumeSorted([1, 2, 3, 4, 5]);
assert(equal(filter!(a => a > 3)(t), assumeSorted([4, 5])));
}

@safe unittest
Expand Down Expand Up @@ -1414,14 +1424,19 @@ Params:
Returns: A range of elements of type $(D Tuple!(ElementType!R, uint)),
representing each consecutively unique element and its respective number of
occurrences in that run. This will be an input range if $(D R) is an input
range, and a forward range in all other cases.
range, and a forward range in all other cases. If a `SortedRanged` is passed,
the result is going to be a `SortedRange`.

See_Also: $(LREF chunkBy), which chunks an input range into subranges
of equivalent adjacent elements.
*/
Group!(pred, Range) group(alias pred = "a == b", Range)(Range r)
auto group(alias pred = "a == b", Range)(Range r)
{
return typeof(return)(r);
import std.range : SortedRange, assumeSorted;
static if (is(Range : SortedRange!TT, TT))
return assumeSorted(Group!(pred, Range)(r));
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@andralex andralex Sep 1, 2017

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same as above

else
return Group!(pred, Range)(r);
}

/// ditto
Expand Down Expand Up @@ -1598,6 +1613,13 @@ if (isInputRange!R)
const(int[][]) a6 = [[1], [1]];
auto g6 = a6.group;
assert(equal(g6.front[0], [1]));

// Issue 9682
import std.range : SortedRange, assumeSorted;
auto a7 = assumeSorted([1, 1, 2, 5, 5, 5, 5]);
auto g7 = a7.group;
static assert(is(typeof(g7) : SortedRange!TT, TT));
assert(equal(g7, [tuple(1, 2u), tuple(2, 1u), tuple(5, 4u)]));
}

// Used by implementation of chunkBy for non-forward input ranges.
Expand Down