[PATCH] D42163: [STLExtras] Add merge_unique

[David Blaikie via llvm-commits]

Should this just be implemented for ranges rather than iterator parameters?

On Wed, Jan 17, 2018 at 12:34 AM Michael Spencer via Phabricator via
llvm-commits <llvm-commits at lists.llvm.org> wrote:

> Bigcheese created this revision.
>
> This is for https://reviews.llvm.org/D36351
>
> This adds the merge_unique algorithm. It's like std::unique except it
> allows modifying the uniqued values.
>
>
> Repository:
>   rL LLVM
>
> https://reviews.llvm.org/D42163
>
> Files:
>   include/llvm/ADT/STLExtras.h
>   unittests/ADT/STLExtrasTest.cpp
>
>
> Index: unittests/ADT/STLExtrasTest.cpp
> ===================================================================
> --- unittests/ADT/STLExtrasTest.cpp
> +++ unittests/ADT/STLExtrasTest.cpp
> @@ -364,4 +364,17 @@
>    EXPECT_EQ(5, count);
>  }
>
> +TEST(STLExtrasTest, merge_unique) {
> +  int a[] = {1, 2, 2, 2, 2, 3, 4, 5, 5};
> +  auto end = merge_unique(std::begin(a), std::end(a),
> +                          [](int a, int b) { return a == b; },
> +                          [](int &a, int b) { a += b; });
> +  EXPECT_EQ(a + 6, end);
> +  EXPECT_EQ(1, a[0]);
> +  EXPECT_EQ(4, a[1]);
> +  EXPECT_EQ(4, a[2]);
> +  EXPECT_EQ(3, a[3]);
> +  EXPECT_EQ(4, a[4]);
> +  EXPECT_EQ(10, a[5]);
> +}
>  } // namespace
> Index: include/llvm/ADT/STLExtras.h
> ===================================================================
> --- include/llvm/ADT/STLExtras.h
> +++ include/llvm/ADT/STLExtras.h
> @@ -932,6 +932,38 @@
>    C.erase(remove_if(C, P), C.end());
>  }
>
> +/// Like `std::unique`, but calls \p Merge on equal values. \p Merge is
> allowed
> +/// to modifiy its first argument.
> +///
> +/// \param Merge a binary callable with a signature callable as
> +///   `Merge(*declval<ForwardIt>(), *declval<ForwardIt>())`
> +///
> +/// Example:
> +///
> +///   int a[] = {1, 2, 2, 3, 4, 5, 5};
> +///   auto end = merge_unique(std::begin(a), std::end(a),
> +///     [](int a, int b) { return a == b; },
> +///     [](int &a, int b) { a += b; });
> +///
> +///   for (auto i = a; i != end; ++i)
> +///     std::cout << *i << " ";
> +///
> +///   -- 1 4 3 4 10
> +template <class ForwardIt, class PredTy, class MergeTy>
> +ForwardIt merge_unique(ForwardIt First, ForwardIt Last, PredTy Pred,
> MergeTy Merge) {
> +  if (First == Last)
> +    return Last;
> +
> +  ForwardIt I = First;
> +  while (++I != Last) {
> +    if (Pred(*First, *I))
> +      Merge(*First, *I);
> +    else if (++First != I)
> +      *First = std::move(*I);
> +  }
> +  return ++First;
> +}
> +
>
>  //===----------------------------------------------------------------------===//
>  //     Extra additions to <memory>
>
>  //===----------------------------------------------------------------------===//
>
>
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