Make SetSampled() setter methood public in TraceOptions (#279)

Author: terencekwt

opencensus/trace/internal/trace_options.cc

@@ -46,5 +46,11 @@ void TraceOptions::SetSampled(bool is_sampled) {
   rep_[0] = (rep_[0] & ~kIsSampled) | (is_sampled ? kIsSampled : 0);
 }
 
+TraceOptions TraceOptions::WithSampling(bool is_sampled) const {
+  TraceOptions child = *this;
+  child.SetSampled(is_sampled);
+  return child;
+}
+
 }  // namespace trace
 }  // namespace opencensus

opencensus/trace/internal/trace_options_test.cc

@@ -48,6 +48,14 @@ TEST(TraceOptionsTest, Comparison) {
   EXPECT_FALSE(a == b);
 }
 
+TEST(TraceOptionsTest, CopyAndSetSampled) {
+  TraceOptions a;
+  SpanTestPeer::SetSampled(&a, true);
+  TraceOptions b = a.WithSampling(false);
+  EXPECT_TRUE(a.IsSampled());
+  EXPECT_FALSE(b.IsSampled());
+}
+
 }  // namespace
 }  // namespace trace
 }  // namespace opencensus

opencensus/trace/trace_options.h

@@ -50,6 +50,10 @@ class TraceOptions final {
   // Copies the TraceOptions data to a buffer, which must hold kSize bytes.
   void CopyTo(uint8_t* buf) const;
 
+  // Returns a copy of these TraceOptions with the sampled bit set to
+  // is_sampled.
+  TraceOptions WithSampling(bool is_sampled) const;
+
  private:
   friend class SpanGenerator;
   friend class SpanTestPeer;