Bug 1295611 - Add mozilla::Span. r=froydnj,gerv.

MozReview-Commit-ID: HGNDClVctbE

mfbt/Casting.h

@@ -238,6 +238,19 @@ AssertedCast(const From aFrom)
   return static_cast<To>(aFrom);
 }
 
+/**
+ * Cast a value of integral type |From| to a value of integral type |To|,
+ * release asserting that the cast will be a safe cast per C++ (that is, that
+ * |to| is in the range of values permitted for the type |From|).
+ */
+template<typename To, typename From>
+inline To
+ReleaseAssertedCast(const From aFrom)
+{
+  MOZ_RELEASE_ASSERT((detail::IsInBounds<From, To>(aFrom)));
+  return static_cast<To>(aFrom);
+}
+
 } // namespace mozilla
 
 #endif /* mozilla_Casting_h */

mfbt/Range.h

@@ -9,6 +9,7 @@
 
 #include "mozilla/RangedPtr.h"
 #include "mozilla/TypeTraits.h"
+#include "mozilla/Span.h"
 
 #include <stddef.h>
 
@@ -44,15 +45,46 @@ class Range
       mEnd(aOther.mEnd)
   {}
 
+  MOZ_IMPLICIT Range(Span<T> aSpan)
+    : Range(aSpan.Elements(), aSpan.Length())
+  {
+  }
+
+  template<typename U,
+           class = typename EnableIf<IsConvertible<U (*)[], T (*)[]>::value,
+                                     int>::Type>
+  MOZ_IMPLICIT Range(const Span<U>& aSpan)
+    : Range(aSpan.Elements(), aSpan.Length())
+  {
+  }
+
   RangedPtr<T> begin() const { return mStart; }
   RangedPtr<T> end() const { return mEnd; }
   size_t length() const { return mEnd - mStart; }
 
   T& operator[](size_t aOffset) const { return mStart[aOffset]; }
 
   explicit operator bool() const { return mStart != nullptr; }
+
+  operator Span<T>() { return Span<T>(mStart.get(), length()); }
+
+  operator Span<const T>() const { return Span<T>(mStart.get(), length()); }
 };
 
+template<class T>
+Span<T>
+MakeSpan(Range<T>& aRange)
+{
+  return aRange;
+}
+
+template<class T>
+Span<const T>
+MakeSpan(const Range<T>& aRange)
+{
+  return aRange;
+}
+
 } // namespace mozilla
 
 #endif /* mozilla_Range_h */