Fix odd UserMetric design in folly/Benchmark.h

Summary: [Folly] Fix odd `UserMetric` design in `folly/Benchmark.h`.

Reviewed By: phoad

Differential Revision: D14494202

fbshipit-source-id: c1be1d9b5bdfe07677713ef00401c85270bbe627

folly/Benchmark.cpp

@@ -323,18 +323,20 @@ class BenchmarkResultsPrinter {
       for (auto const& name : counterNames_) {
         if (auto ptr = folly::get_ptr(datum.counters, name)) {
           switch (ptr->type) {
-            case UserMetric::TIME:
+            case UserMetric::Type::TIME:
               printf(
-                  "  %-*s", int(name.length()), readableTime(*ptr, 2).c_str());
+                  "  %-*s",
+                  int(name.length()),
+                  readableTime(ptr->value, 2).c_str());
               break;
-            case UserMetric::METRIC:
+            case UserMetric::Type::METRIC:
               printf(
                   "  %-*s",
                   int(name.length()),
-                  metricReadable(*ptr, 2).c_str());
+                  metricReadable(ptr->value, 2).c_str());
               break;
             default:
-              printf("  %-*d", int(name.length()), (int)*ptr);
+              printf("  %-*d", int(name.length()), ptr->value);
           }
         } else {
           printf("  %-*s", int(name.length()), "NaN");

folly/Benchmark.h

@@ -53,20 +53,16 @@ inline bool runBenchmarksOnFlag() {
   return FLAGS_benchmark;
 }
 
-struct UserMetric {
-  enum Type { CUSTOM, TIME, METRIC };
-  int value;
-  Type type{CUSTOM};
+class UserMetric {
+ public:
+  enum class Type { CUSTOM, TIME, METRIC };
+
+  int value{};
+  Type type{Type::CUSTOM};
+
   UserMetric() = default;
-  template <typename T>
-  /* implicit */ UserMetric(T val, Type typ = CUSTOM)
-      : value(static_cast<int>(val)), type(typ) {}
-  operator int() const {
-    return value;
-  }
-  operator int&() {
-    return value;
-  }
+  /* implicit */ UserMetric(int val, Type typ = Type::CUSTOM)
+      : value(val), type(typ) {}
 };
 
 using UserCounters = std::unordered_map<std::string, UserMetric>;