Bug 1577700 - Add a function for obtaining a Span of char from a Span of uint8_t. r=froydnj

Differential Revision: https://phabricator.services.mozilla.com/D44124

--HG--
extra : moz-landing-system : lando

mfbt/Span.h

@@ -808,6 +808,20 @@ AsWritableBytes(Span<ElementType, Extent> s) {
   return {reinterpret_cast<uint8_t*>(s.data()), s.size_bytes()};
 }
 
+/**
+ * View a span of uint8_t as a span of char.
+ */
+inline Span<const char> AsChars(Span<const uint8_t> s) {
+  return {reinterpret_cast<const char*>(s.data()), s.size()};
+}
+
+/**
+ * View a writable span of uint8_t as a span of char.
+ */
+inline Span<char> AsWritableChars(Span<uint8_t> s) {
+  return {reinterpret_cast<char*>(s.data()), s.size()};
+}
+
 //
 // MakeSpan() - Utility functions for creating Spans
 //

mfbt/tests/gtest/TestSpan.cpp

@@ -1965,6 +1965,23 @@ SPAN_TEST(as_writable_bytes) {
   }
 }
 
+SPAN_TEST(as_chars) {
+  const uint8_t a[] = {1, 2, 3, 4};
+  Span<const uint8_t> u = MakeSpan(a);
+  Span<const char> c = AsChars(u);
+  ASSERT_EQ(static_cast<const void*>(u.data()),
+            static_cast<const void*>(c.data()));
+  ASSERT_EQ(u.size(), c.size());
+}
+
+SPAN_TEST(as_writable_chars) {
+  uint8_t a[] = {1, 2, 3, 4};
+  Span<uint8_t> u = MakeSpan(a);
+  Span<char> c = AsWritableChars(u);
+  ASSERT_EQ(static_cast<void*>(u.data()), static_cast<void*>(c.data()));
+  ASSERT_EQ(u.size(), c.size());
+}
+
 SPAN_TEST(fixed_size_conversions) {
   int arr[] = {1, 2, 3, 4};