Improve Summary and Histogram API. Add constructors from rvalue refer…

…ences, observe from templated input it

core/include/prometheus/histogram.h

@@ -1,6 +1,8 @@
 #pragma once
 
+#include <cstddef>
 #include <mutex>
+#include <stdexcept>
 #include <vector>
 
 #include "prometheus/client_metric.h"
@@ -62,7 +64,28 @@ class PROMETHEUS_CPP_CORE_EXPORT Histogram {
   /// this function must have already sorted the values into buckets).
   /// Also increments the total sum of all observations by the given value.
   void ObserveMultiple(const std::vector<double>& bucket_increments,
-                       const double sum_of_values);
+                       double sum_of_values);
+
+  /// Same as above with custom iterator type.
+  template <class InputIt>
+  void ObserveMultiple(InputIt from, InputIt end, double sum_of_values) {
+    std::lock_guard<std::mutex> lock(mutex_);
+    sum_.Increment(sum_of_values);
+
+    for (std::size_t i{0}; i < bucket_counts_.size(); ++i, ++from) {
+      if (from == end) {
+        throw std::length_error(
+            "The size of bucket_increments should be equal to "
+            "the number of buckets in the histogram.");
+      }
+      bucket_counts_[i].Increment(*from);
+    }
+    if (from != end) {
+      throw std::length_error(
+          "The size of bucket_increments should be equal to "
+          "the number of buckets in the histogram.");
+    }
+  }
 
   /// \brief Get the current value of the histogram.
   ///

core/tests/histogram_test.cc

@@ -2,6 +2,7 @@
 
 #include <gtest/gtest.h>
 
+#include <forward_list>
 #include <limits>
 #include <memory>
 #include <stdexcept>
@@ -89,7 +90,7 @@ TEST(HistogramTest, cumulative_bucket_count) {
   EXPECT_EQ(h.bucket.at(2).cumulative_count, 7U);
 }
 
-TEST(HistogramTest, observe_multiple_test_bucket_counts) {
+TEST(HistogramTest, observe_multiple_test_bucket_counts_1) {
   Histogram histogram{{1, 2}};
   histogram.ObserveMultiple({5, 9, 3}, 20);
   histogram.ObserveMultiple({0, 20, 6}, 34);
@@ -101,6 +102,20 @@ TEST(HistogramTest, observe_multiple_test_bucket_counts) {
   EXPECT_EQ(h.bucket.at(2).cumulative_count, 43U);
 }
 
+TEST(HistogramTest, observe_multiple_test_bucket_counts_2) {
+  Histogram histogram{{1, 2}};
+  const std::forward_list<double> values1 = {5, 9, 3};
+  const std::forward_list<double> values2 = {0, 20, 6};
+  histogram.ObserveMultiple(values1.begin(), values1.end(), 20);
+  histogram.ObserveMultiple(values2.begin(), values2.end(), 34);
+  auto metric = histogram.Collect();
+  auto h = metric.histogram;
+  ASSERT_EQ(h.bucket.size(), 3U);
+  EXPECT_EQ(h.bucket.at(0).cumulative_count, 5U);
+  EXPECT_EQ(h.bucket.at(1).cumulative_count, 34U);
+  EXPECT_EQ(h.bucket.at(2).cumulative_count, 43U);
+}
+
 TEST(HistogramTest, observe_multiple_test_total_sum) {
   Histogram histogram{{1, 2}};
   histogram.ObserveMultiple({5, 9, 3}, 20);
@@ -111,13 +126,23 @@ TEST(HistogramTest, observe_multiple_test_total_sum) {
   EXPECT_EQ(h.sample_sum, 54);
 }
 
-TEST(HistogramTest, observe_multiple_test_length_error) {
+TEST(HistogramTest, observe_multiple_test_length_error1) {
   Histogram histogram{{1, 2}};
   // 2 bucket boundaries means there are 3 buckets, so giving just 2 bucket
   // increments should result in a length_error.
   ASSERT_THROW(histogram.ObserveMultiple({5, 9}, 20), std::length_error);
 }
 
+TEST(HistogramTest, observe_multiple_test_length_error2) {
+  Histogram histogram{{1, 2}};
+  const std::forward_list<double> values1 = {5, 9};
+  ASSERT_THROW(histogram.ObserveMultiple(values1.begin(), values1.end(), 20),
+               std::length_error);
+  const std::forward_list<double> values2 = {5, 9, 5, 6};
+  ASSERT_THROW(histogram.ObserveMultiple(values2.begin(), values2.end(), 20),
+               std::length_error);
+}
+
 TEST(HistogramTest, sum_can_go_down) {
   Histogram histogram{{1}};
   auto metric1 = histogram.Collect();