TagMap: assert() on duplicate keys in constructor in debug builds. (#219)

Author: g-easy

opencensus/tags/internal/tag_map.cc

@@ -14,6 +14,8 @@
 
 #include "opencensus/tags/tag_map.h"
 
+#include <algorithm>
+#include <cassert>
 #include <functional>
 #include <initializer_list>
 #include <string>
@@ -46,6 +48,14 @@ TagMap::TagMap(std::vector<std::pair<TagKey, std::string>> tags)
 void TagMap::Initialize() {
   std::sort(tags_.begin(), tags_.end());
 
+  auto compare_keys = [](const std::pair<TagKey, std::string>& a,
+                         const std::pair<TagKey, std::string>& b) {
+    return a.first == b.first;
+  };
+  assert(std::adjacent_find(tags_.begin(), tags_.end(), compare_keys) ==
+             tags_.end() &&
+         "Duplicate keys are not allowed in TagMap.");
+
   std::hash<std::string> hasher;
   common::HashMix mixer;
   for (const auto& tag : tags_) {

opencensus/tags/internal/tag_map_test.cc

@@ -104,6 +104,15 @@ TEST(TagMapTest, DebugStringContainsTags) {
   EXPECT_THAT(s, HasSubstr("value2"));
 }
 
+TEST(TagMapDeathTest, DuplicateKeysNotAllowed) {
+  TagKey k = TagKey::Register("k");
+  EXPECT_DEBUG_DEATH(
+      {
+        TagMap m({{k, "v1"}, {k, "v2"}});
+      },
+      "Duplicate keys are not allowed");
+}
+
 }  // namespace
 }  // namespace tags
 }  // namespace opencensus