introduce edm::Span

DataFormats/NanoAOD/interface/FlatTable.h

@@ -3,7 +3,7 @@
 
 #include "DataFormats/Math/interface/libminifloat.h"
 #include "FWCore/Utilities/interface/Exception.h"
-#include "FWCore/Utilities/interface/Range.h"
+#include "FWCore/Utilities/interface/Span.h"
 
 #include <cstdint>
 #include <vector>
@@ -17,8 +17,8 @@ namespace nanoaod {
     struct MaybeMantissaReduce {
       MaybeMantissaReduce(int mantissaBits) {}
       inline T one(const T &val) const { return val; }
-      template <typename Range>
-      inline void bulk(Range &&data) const {}
+      template <typename Span>
+      inline void bulk(Span &&data) const {}
     };
     template <>
     struct MaybeMantissaReduce<float> {
@@ -27,8 +27,8 @@ namespace nanoaod {
       inline float one(const float &val) const {
         return (bits_ > 0 ? MiniFloatConverter::reduceMantissaToNbitsRounding(val, bits_) : val);
       }
-      template <typename Range>
-      inline void bulk(Range &&data) const {
+      template <typename Span>
+      inline void bulk(Span &&data) const {
         if (bits_ > 0)
           MiniFloatConverter::reduceMantissaToNbitsRounding(bits_, data.begin(), data.end(), data.begin());
       }
@@ -69,14 +69,14 @@ namespace nanoaod {
     template <typename T>
     auto columnData(unsigned int column) const {
       auto begin = beginData<T>(column);
-      return edm::Range(begin, begin + size_);
+      return edm::Span(begin, begin + size_);
     }
 
     /// get a column by index (non-const)
     template <typename T>
     auto columnData(unsigned int column) {
       auto begin = beginData<T>(column);
-      return edm::Range(begin, begin + size_);
+      return edm::Span(begin, begin + size_);
     }
 
     /// get a column value for singleton (const)

FWCore/Utilities/interface/Range.h

@@ -1,8 +1,6 @@
 #ifndef FWCore_Utilities_Range_h
 #define FWCore_Utilities_Range_h
 
-#include <cstddef>
-
 namespace edm {
   /*
       *class which implements begin() and end() to use range-based loop with
@@ -18,12 +16,6 @@ namespace edm {
     T end() const { return end_; }
 
     bool empty() const { return begin_ == end_; }
-    auto size() const { return end_ - begin_; }
-
-    auto const& operator[](std::size_t idx) const { return *(begin_ + idx); }
-
-    auto const& front() const { return *begin_; }
-    auto const& back() const { return *(end_ - 1); }
 
   private:
     const T begin_;

FWCore/Utilities/interface/Span.h

@@ -0,0 +1,37 @@
+#ifndef FWCore_Utilities_Span_h
+#define FWCore_Utilities_Span_h
+
+#include <cstddef>
+
+namespace edm {
+  /*
+      *An edm::Span wraps begin() and end() iterators to a contiguous sequence
+      of objects with the first element of the sequence at position zero,
+      In other words the iterators should refer to random-access containers.
+
+      To be replaced with std::Span in C++20.
+      */
+
+  template <class T>
+  class Span {
+  public:
+    Span(T begin, T end) : begin_(begin), end_(end) {}
+
+    T begin() const { return begin_; }
+    T end() const { return end_; }
+
+    bool empty() const { return begin_ == end_; }
+    auto size() const { return end_ - begin_; }
+
+    auto const& operator[](std::size_t idx) const { return *(begin_ + idx); }
+
+    auto const& front() const { return *begin_; }
+    auto const& back() const { return *(end_ - 1); }
+
+  private:
+    const T begin_;
+    const T end_;
+  };
+};  // namespace edm
+
+#endif