Merge pull request #4347 from romainbrenguier/feature/range-drop

Add ranget drop and skip methods

Author: romainbrenguier

src/util/range.h

@@ -289,7 +289,8 @@ struct ranget final
 public:
   using value_type = typename iteratort::value_type;
 
-  ranget(iteratort begin, iteratort end) : begin_value(begin), end_value(end)
+  ranget(iteratort begin, iteratort end)
+    : begin_value(std::move(begin)), end_value(std::move(end))
   {
   }
 
@@ -341,6 +342,24 @@ struct ranget final
     return begin_value == end_value;
   }
 
+  /// Return an new range containing the same elements except for the first
+  /// \p count elements.
+  /// If the range has fewer elements, returns an empty range.
+  ranget<iteratort> drop(std::size_t count) &&
+  {
+    for(; count > 0 && begin_value != end_value; --count)
+      ++begin_value;
+    return ranget<iteratort>{std::move(begin_value), std::move(end_value)};
+  }
+
+  /// Return an new range containing the same elements except for the first
+  /// \p count elements.
+  /// If the range has fewer elements, returns an empty range.
+  ranget<iteratort> drop(std::size_t count) const &
+  {
+    return ranget<iteratort>{begin(), end()}.drop(count);
+  }
+
   iteratort begin() const
   {
     return begin_value;

unit/util/range.cpp

@@ -57,6 +57,45 @@ SCENARIO("range tests", "[core][util][range]")
       ++it;
       REQUIRE(it == filtered_range.end());
     }
+
+    THEN("Drop first 2 elements")
+    {
+      auto range = make_range(list);
+      auto drop_range = range.drop(2);
+      auto it = drop_range.begin();
+      REQUIRE(*it == "acdef");
+      drop_range = std::move(drop_range).drop(1);
+      REQUIRE(drop_range.empty());
+      // Check the original is unmodified
+      REQUIRE(!range.empty());
+      REQUIRE(*range.begin() == "abc");
+    }
+    THEN("Drop first 5 elements")
+    {
+      auto range = make_range(list);
+      auto skip_range = range.drop(5);
+      REQUIRE(skip_range.empty());
+      // Check the original is unmodified
+      REQUIRE(!range.empty());
+      REQUIRE(*range.begin() == "abc");
+    }
+    THEN("Drop first 2 elements, move version")
+    {
+      auto range = make_range(list);
+      range = std::move(range).drop(2);
+      REQUIRE(!range.empty());
+      auto it = range.begin();
+      REQUIRE(*it == "acdef");
+      range = std::move(range).drop(1);
+      REQUIRE(range.empty());
+    }
+    THEN("Drop first 5 elements, move version")
+    {
+      auto range = make_range(list);
+      range = std::move(range).drop(5);
+      REQUIRE(range.empty());
+    }
+
     THEN(
       "A const instance of a `filter_iteratort` can mutate the input "
       "collection.")