Promote DigestBuilder out of detail

Summary: `DigestBuilder` is a useful companion to `TDigest` (already public), has a simple and well-defined interface, better documentation than most classes in the parent directory, tests, and benchmarks. It doesn't need to be in `detail/`, and it can be useful for use cases not covered by `BufferedStat`, for example when sub-second resolution and a precise flush schedule are required.

Reviewed By: philippv, luciang

Differential Revision: D31643638

fbshipit-source-id: 4f2f54a933942cbe02d08cd63ab5fc04f13630e3

folly/stats/detail/DigestBuilder-inl.h → folly/stats/DigestBuilder-inl.h

@@ -21,7 +21,6 @@
 #include <folly/concurrency/CacheLocality.h>
 
 namespace folly {
-namespace detail {
 
 template <typename DigestT>
 DigestBuilder<DigestT>::DigestBuilder(size_t bufferSize, size_t digestSize)
@@ -82,5 +81,4 @@ void DigestBuilder<DigestT>::append(double value) {
   }
 }
 
-} // namespace detail
 } // namespace folly

folly/stats/detail/DigestBuilder.h → folly/stats/DigestBuilder.h

@@ -22,7 +22,6 @@
 #include <folly/SpinLock.h>
 
 namespace folly {
-namespace detail {
 
 /*
  * Stat digests, such as TDigest, can be expensive to merge. It is faster to
@@ -72,7 +71,6 @@ class DigestBuilder {
   size_t digestSize_;
 };
 
-} // namespace detail
 } // namespace folly
 
-#include <folly/stats/detail/DigestBuilder-inl.h>
+#include <folly/stats/DigestBuilder-inl.h>

folly/stats/detail/BufferedStat.h

@@ -17,7 +17,7 @@
 #pragma once
 
 #include <folly/SharedMutex.h>
-#include <folly/stats/detail/DigestBuilder.h>
+#include <folly/stats/DigestBuilder.h>
 #include <folly/stats/detail/SlidingWindow.h>
 
 namespace folly {

folly/stats/test/DigestBuilderBenchmark.cpp

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-#include <folly/stats/detail/DigestBuilder.h>
+#include <folly/stats/DigestBuilder.h>
 
 #include <chrono>
 #include <condition_variable>
@@ -29,7 +29,6 @@
 DEFINE_int32(digest_merge_time_ns, 5500, "Time to merge into the digest");
 
 using namespace folly;
-using namespace folly::detail;
 
 class FreeDigest {
  public:

folly/stats/test/DigestBuilderTest.cpp

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-#include <folly/stats/detail/DigestBuilder.h>
+#include <folly/stats/DigestBuilder.h>
 
 #include <chrono>
 #include <random>
@@ -24,7 +24,6 @@
 #include <folly/portability/GTest.h>
 
 using namespace folly;
-using namespace folly::detail;
 
 template <size_t MergeSize>
 class SimpleDigest {