src: make ToLower/ToUpper input args more flexible

In particular, this enables passing `std::string_view` instead.

Author: addaleax

src/util-inl.h

@@ -194,21 +194,29 @@ char ToLower(char c) {
   return std::tolower(c, std::locale::classic());
 }
 
-std::string ToLower(const std::string& in) {
-  std::string out(in.size(), 0);
-  for (size_t i = 0; i < in.size(); ++i)
-    out[i] = ToLower(in[i]);
+template <typename T>
+std::string ToLower(const T& in) {
+  auto it = std::cbegin(in);
+  auto end = std::cend(in);
+  std::string out(std::distance(it, end), 0);
+  size_t i;
+  for (i = 0; it != end; ++it, ++i) out[i] = ToLower(*it);
+  DCHECK_EQ(i, out.size());
   return out;
 }
 
 char ToUpper(char c) {
   return std::toupper(c, std::locale::classic());
 }
 
-std::string ToUpper(const std::string& in) {
-  std::string out(in.size(), 0);
-  for (size_t i = 0; i < in.size(); ++i)
-    out[i] = ToUpper(in[i]);
+template <typename T>
+std::string ToUpper(const T& in) {
+  auto it = std::cbegin(in);
+  auto end = std::cend(in);
+  std::string out(std::distance(it, end), 0);
+  size_t i;
+  for (i = 0; it != end; ++it, ++i) out[i] = ToUpper(*it);
+  DCHECK_EQ(i, out.size());
   return out;
 }
 

src/util.h

@@ -366,11 +366,13 @@ inline v8::Local<v8::String> FIXED_ONE_BYTE_STRING(v8::Isolate* isolate,
 
 // tolower() is locale-sensitive.  Use ToLower() instead.
 inline char ToLower(char c);
-inline std::string ToLower(const std::string& in);
+template <typename T>
+inline std::string ToLower(const T& in);
 
 // toupper() is locale-sensitive.  Use ToUpper() instead.
 inline char ToUpper(char c);
-inline std::string ToUpper(const std::string& in);
+template <typename T>
+inline std::string ToUpper(const T& in);
 
 // strcasecmp() is locale-sensitive.  Use StringEqualNoCase() instead.
 inline bool StringEqualNoCase(const char* a, const char* b);