More changes to the ANTLRInputStream and ANTLRFileStream classes

- Added a default c-tor to the input stream to avoid an ambiquity.
- Changed the input stream API so that it can take a string pointer + length and use that for UTF conversion, avoiding so unnecessary copies. Convenience methods exist to use a std::string or a std::string_view.
- With that only a single load() method is necessary.
- In ANTLRFileStream the other c-tors are now also deleted, as they make no sense there.

runtime/Cpp/runtime/src/ANTLRFileStream.cpp

@@ -9,9 +9,6 @@
 
 using namespace antlr4;
 
-ANTLRFileStream::ANTLRFileStream(): ANTLRInputStream(std::string()) {
-}
-
 void ANTLRFileStream::loadFromFile(const std::string &fileName) {
   _fileName = fileName;
   if (_fileName.empty()) {

runtime/Cpp/runtime/src/ANTLRFileStream.h

@@ -14,8 +14,9 @@ namespace antlr4 {
   // TODO: this class needs testing.
   class ANTLR4CPP_PUBLIC ANTLRFileStream : public ANTLRInputStream {
   public:
-    ANTLRFileStream();
     ANTLRFileStream(const std::string &) = delete;
+    ANTLRFileStream(const char *data, size_t length) = delete;
+    ANTLRFileStream(std::istream &stream) = delete;
 
     // Assumes a file name encoded in UTF-8 and file content in the same encoding (with or w/o BOM).
     virtual void loadFromFile(const std::string &fileName);

runtime/Cpp/runtime/src/ANTLRInputStream.cpp

@@ -17,47 +17,41 @@ using namespace antlrcpp;
 
 using misc::Interval;
 
-#if __cplusplus >= 201703L
-ANTLRInputStream::ANTLRInputStream(std::string_view input) {
+ANTLRInputStream::ANTLRInputStream() {
   InitializeInstanceFields();
-  load(input);
+}
+
+#if __cplusplus >= 201703L
+ANTLRInputStream::ANTLRInputStream(const std::string_view &input): ANTLRInputStream() {
+  load(input.data(), input.length());
 }
 #endif
 
-ANTLRInputStream::ANTLRInputStream(const std::string &input) {
-  InitializeInstanceFields();
-  load(input);
+ANTLRInputStream::ANTLRInputStream(const std::string &input): ANTLRInputStream() {
+  load(input.data(), input.size());
 }
 
-ANTLRInputStream::ANTLRInputStream(const char data_[], size_t numberOfActualCharsInArray)
-  : ANTLRInputStream(std::string(data_, numberOfActualCharsInArray)) {
+ANTLRInputStream::ANTLRInputStream(const char *data, size_t length) {
+  load(data, length);
 }
 
-ANTLRInputStream::ANTLRInputStream(std::istream &stream) {
-  InitializeInstanceFields();
+ANTLRInputStream::ANTLRInputStream(std::istream &stream): ANTLRInputStream() {
   load(stream);
 }
 
-#if __cplusplus >= 201703L
-void ANTLRInputStream::load(std::string_view input) {
-  // Remove the UTF-8 BOM if present.
-  constexpr std::string_view bom = "\xef\xbb\xbf";
-  if (input.compare(0, 3, bom) == 0)
-    input.remove_prefix(3);
-  _data = antlrcpp::utf8_to_utf32(input.data(), input.data() + input.size());
-  p = 0;
-}
-#else
 void ANTLRInputStream::load(const std::string &input) {
+  load(input.data(), input.size());
+}
+
+void ANTLRInputStream::load(const char *data, size_t length) {
   // Remove the UTF-8 BOM if present.
   const char bom[4] = "\xef\xbb\xbf";
-  if (input.compare(0, 3, bom, 3) == 0)
-    _data = antlrcpp::utf8_to_utf32(input.data() + 3, input.data() + input.size());
+  if (strncmp(data, bom, 3) == 0)
+    _data = antlrcpp::utf8_to_utf32(data + 3, data + length);
   else
-    _data = antlrcpp::utf8_to_utf32(input.data(), input.data() + input.size());
+    _data = antlrcpp::utf8_to_utf32(data, data + length);
   p = 0;
 }
-#endif
 
 void ANTLRInputStream::load(std::istream &stream) {
   if (!stream.good() || stream.eof()) // No fail, bad or EOF.
@@ -66,7 +60,7 @@ void ANTLRInputStream::load(std::istream &stream) {
   _data.clear();
 
   std::string s((std::istreambuf_iterator<char>(stream)), std::istreambuf_iterator<char>());
-  load(s);
+  load(s.data(), s.length());
 }
 
 void ANTLRInputStream::reset() {

runtime/Cpp/runtime/src/ANTLRInputStream.h

@@ -25,18 +25,18 @@ namespace antlr4 {
     /// What is name or source of this char stream?
     std::string name;
 
-#if __cplusplus >= 201703L
-    ANTLRInputStream(std::string_view input = "");
-#endif
-    ANTLRInputStream(const std::string &input = "");
-    ANTLRInputStream(const char data_[], size_t numberOfActualCharsInArray);
-    ANTLRInputStream(std::istream &stream);
+    ANTLRInputStream();
     
 #if __cplusplus >= 201703L
-    virtual void load(std::string_view input);
-#else
-    virtual void load(const std::string &input);
+    ANTLRInputStream(const std::string_view &input);
 #endif
+    
+    ANTLRInputStream(const std::string &input);
+    ANTLRInputStream(const char *data, size_t length);
+    ANTLRInputStream(std::istream &stream);
+
+    virtual void load(const std::string &input);
+    virtual void load(const char *data, size_t length);
     virtual void load(std::istream &stream);
 
     /// Reset the stream so that it's in the same state it was