Make ContextValue default constructible with monostate (#731)

open-telemetry · May 13, 2021 · 414a731 · 414a731
1 parent 834bba6
commit 414a731
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Showing 6 changed files with 16 additions and 18 deletions.
diff --git a/api/include/opentelemetry/context/context.h b/api/include/opentelemetry/context/context.h
@@ -72,23 +72,13 @@ class Context
         }
       }
     }
-    return (int64_t)0;
+    return ContextValue{};
   }
 
   // Checks for key and returns true if found
   bool HasKey(const nostd::string_view key) const noexcept
   {
-    for (DataList *data = head_.get(); data != nullptr; data = data->next_.get())
-    {
-      if (key.size() == data->key_length_)
-      {
-        if (std::memcmp(key.data(), data->key_, data->key_length_) == 0)
-        {
-          return true;
-        }
-      }
-    }
-    return false;
+    return !nostd::holds_alternative<nostd::monostate>(GetValue(key));
   }
 
   bool operator==(const Context &other) const noexcept { return (head_ == other.head_); }

diff --git a/api/include/opentelemetry/context/context_value.h b/api/include/opentelemetry/context/context_value.h
@@ -13,7 +13,8 @@
 OPENTELEMETRY_BEGIN_NAMESPACE
 namespace context
 {
-using ContextValue = nostd::variant<bool,
+using ContextValue = nostd::variant<nostd::monostate,
+                                    bool,
                                     int64_t,
                                     uint64_t,
                                     double,

diff --git a/api/include/opentelemetry/nostd/variant.h b/api/include/opentelemetry/nostd/variant.h
@@ -39,7 +39,9 @@ namespace nostd
 {
 using absl::get;
 using absl::holds_alternative;
+using absl::monostate;
 using absl::variant;
+using absl::variant_size;
 using absl::visit;
 
 // nostd::bad_variant_access

diff --git a/api/include/opentelemetry/std/variant.h b/api/include/opentelemetry/std/variant.h
@@ -33,6 +33,8 @@ using variant = std::variant<_Types...>;
 template <class... _Types>
 using variant_size = std::variant_size<_Types...>;
 
+using monostate = std::monostate;
+
 #if defined(__APPLE__) && defined(_LIBCPP_USE_AVAILABILITY_APPLE)
 // Apple Platforms provide std::bad_variant_access only in newer versions of OS.
 // To keep API compatible with any version of OS - we are providing our own

diff --git a/api/test/context/context_test.cc b/api/test/context/context_test.cc
@@ -58,7 +58,7 @@ TEST(ContextTest, ContextImmutability)
   context::Context context_test = context::Context(map_test);
   context::Context context_foo  = context_test.SetValue("foo_key", (int64_t)456);
 
-  EXPECT_NE(nostd::get<int64_t>(context_test.GetValue("foo_key")), 456);
+  EXPECT_FALSE(nostd::holds_alternative<int64_t>(context_test.GetValue("foo_key")));
 }
 
 // Tests that writing the same to a context overwrites the original value.
@@ -89,8 +89,8 @@ TEST(ContextTest, ContextInheritance)
   EXPECT_EQ(nostd::get<int64_t>(foo_context.GetValue("other_key")), 789);
   EXPECT_EQ(nostd::get<int64_t>(foo_context.GetValue("another_key")), 987);
 
-  EXPECT_EQ(nostd::get<int64_t>(test_context.GetValue("other_key")), 0);
-  EXPECT_EQ(nostd::get<int64_t>(test_context.GetValue("another_key")), 0);
+  EXPECT_TRUE(nostd::holds_alternative<nostd::monostate>(test_context.GetValue("other_key")));
+  EXPECT_TRUE(nostd::holds_alternative<nostd::monostate>(test_context.GetValue("another_key")));
 }
 
 // Tests that copying a context copies the key value pairs as expected.

diff --git a/sdk/src/common/core.cc b/sdk/src/common/core.cc
@@ -1,7 +1,10 @@
-#include "opentelemetry/nostd/variant.h"
+// clang-format off
+// version.h should be included before nostd/variant.h.
 #include "opentelemetry/version.h"
+#include "opentelemetry/nostd/variant.h"
+// clang-format on
 
-#if defined(HAVE_ABSEIL)
+#if defined(HAVE_ABSEIL) && !defined(HAVE_ABSEIL_VARIANT)
 
 #  if defined(__GNUC__) || defined(__GNUG__)
 #    ifndef __cdecl