Add data() method to folly sorted vector types

Summary: Add a data() method to folly::sorted_vector_map and folly::sorted_vector_set which returns a const pointer to the underlying container's data

Reviewed By: yfeldblum

Differential Revision: D8750840

fbshipit-source-id: d361fe21ac741b31b60f551935a3ed8c9549f11a

folly/sorted_vector_types.h

@@ -487,6 +487,10 @@ class sorted_vector_set
     return m_.cont_ < other.m_.cont_;
   }
 
+  const value_type* data() const noexcept {
+    return m_.cont_.data();
+  }
+
  private:
   /*
    * This structure derives from the comparison object in order to
@@ -840,6 +844,10 @@ class sorted_vector_map
     return m_.cont_ < other.m_.cont_;
   }
 
+  const value_type* data() const noexcept {
+    return m_.cont_.data();
+  }
+
  private:
   // This is to get the empty base optimization; see the comment in
   // sorted_vector_set.

folly/test/sorted_vector_test.cpp

@@ -773,3 +773,18 @@ TEST(SortedVectorTypes, TestBulkInsertionWithDuplicatesIntoEmptySet) {
   }
   EXPECT_THAT(set, testing::ElementsAreArray({0, 1}));
 }
+
+TEST(SortedVectorTypes, TestDataPointsToFirstElement) {
+  sorted_vector_set<int> set;
+  sorted_vector_map<int, int> map;
+
+  set.insert(0);
+  map[0] = 0;
+  EXPECT_EQ(set.data(), &*set.begin());
+  EXPECT_EQ(map.data(), &*map.begin());
+
+  set.insert(1);
+  map[1] = 1;
+  EXPECT_EQ(set.data(), &*set.begin());
+  EXPECT_EQ(map.data(), &*map.begin());
+}