Adding comments

Author: cgilmour

src/datadog/metrics.h

@@ -8,9 +8,17 @@ namespace datadog {
 namespace tracing {
 
 class Metric {
+  // The name of the metric that will be published. A transformation occurs
+  // based on the name and whether it is "common" or "language-specific" when it
+  // is recorded.
   const std::string name_;
+  // The type of the metric. This will currently be count or gauge.
   const std::string type_;
+  // Tags associated with this specific instance of the metric.
   const std::vector<std::string> tags_;
+  // This affects the transformation of the metric name, where it can be a
+  // common telemetry metric, or a language-specific metric that is prefixed
+  // with the language name.
   bool common_;
 
  protected:
@@ -19,6 +27,8 @@ class Metric {
          const std::vector<std::string> tags, bool common);
 
  public:
+  // Accessors for name, type, tags, common and value are used when producing
+  // the JSON message for reporting metrics.
   const std::string name();
   const std::string type();
   const std::vector<std::string> tags();

src/datadog/tracer_telemetry.h

@@ -12,9 +12,11 @@ class TracerTelemetry {
   FinalizedTracerConfig config_;
   uint64_t seq_id = 0;
   using MetricSnapshot = std::vector<std::pair<time_t, uint64_t>>;
+  // This uses a reference_wrapper so references to internal metric values can
+  // be captured, and be iterated trivially when the values need to be
+  // snapshotted and published in telemetry messages.
   std::vector<std::pair<std::reference_wrapper<Metric>, MetricSnapshot>>
       metrics_snapshots_;
-
   struct {
     struct {
       CounterMetric spans_created = {