emitter: Support std::string_view

Accept Emitter::operator<<(std::string_view).

ABI remains C++11 compatible by exposing new method
Emitter::Write(const char*, size_t).

All affected calls optimized to pass std::string values as pointer + size
tuple into appropriate routines.

Author: Daniel Levin

include/yaml-cpp/emitter.h

@@ -9,12 +9,17 @@
 
 #include <cmath>
 #include <cstddef>
+#include <cstring>
 #include <limits>
 #include <memory>
 #include <sstream>
 #include <string>
 #include <type_traits>
 
+#if ((defined(_MSVC_LANG) && _MSVC_LANG >= 201703L) || __cplusplus >= 201703L)
+#include <string_view>
+#endif
+
 #include "yaml-cpp/binary.h"
 #include "yaml-cpp/dll.h"
 #include "yaml-cpp/emitterdef.h"
@@ -68,6 +73,7 @@ class YAML_CPP_API Emitter {
   Emitter& SetLocalPrecision(const _Precision& precision);
 
   // overloads of write
+  Emitter& Write(const char* str, std::size_t size);
   Emitter& Write(const std::string& str);
   Emitter& Write(bool b);
   Emitter& Write(char ch);
@@ -201,8 +207,13 @@ inline void Emitter::SetStreamablePrecision<double>(std::stringstream& stream) {
 }
 
 // overloads of insertion
+#if ((defined(_MSVC_LANG) && _MSVC_LANG >= 201703L) || __cplusplus >= 201703L)
+inline Emitter& operator<<(Emitter& emitter, const std::string_view& v) {
+  return emitter.Write(v.data(), v.size());
+}
+#endif
 inline Emitter& operator<<(Emitter& emitter, const std::string& v) {
-  return emitter.Write(v);
+  return emitter.Write(v.data(), v.size());
 }
 inline Emitter& operator<<(Emitter& emitter, bool v) {
   return emitter.Write(v);
@@ -233,7 +244,7 @@ inline Emitter& operator<<(Emitter& emitter, const Binary& b) {
 }
 
 inline Emitter& operator<<(Emitter& emitter, const char* v) {
-  return emitter.Write(std::string(v));
+  return emitter.Write(v, std::strlen(v));
 }
 
 inline Emitter& operator<<(Emitter& emitter, int v) {

include/yaml-cpp/null.h

@@ -8,7 +8,7 @@
 #endif
 
 #include "yaml-cpp/dll.h"
-#include <string>
+#include <cstddef>
 
 namespace YAML {
 class Node;
@@ -18,7 +18,7 @@ inline bool operator==(const _Null&, const _Null&) { return true; }
 inline bool operator!=(const _Null&, const _Null&) { return false; }
 
 YAML_CPP_API bool IsNull(const Node& node);  // old API only
-YAML_CPP_API bool IsNullString(const std::string& str);
+YAML_CPP_API bool IsNullString(const char* str, std::size_t size);
 
 extern YAML_CPP_API _Null Null;
 }

src/emitter.cpp

@@ -716,33 +716,33 @@ StringEscaping::value GetStringEscapingStyle(const EMITTER_MANIP emitterManip) {
   }
 }
 
-Emitter& Emitter::Write(const std::string& str) {
+Emitter& Emitter::Write(const char* str, std::size_t size) {
   if (!good())
     return *this;
 
   StringEscaping::value stringEscaping = GetStringEscapingStyle(m_pState->GetOutputCharset());
 
   const StringFormat::value strFormat =
-      Utils::ComputeStringFormat(str, m_pState->GetStringFormat(),
+      Utils::ComputeStringFormat(str, size, m_pState->GetStringFormat(),
                                  m_pState->CurGroupFlowType(), stringEscaping == StringEscaping::NonAscii);
 
-  if (strFormat == StringFormat::Literal || str.size() > 1024)
+  if (strFormat == StringFormat::Literal || size > 1024)
     m_pState->SetMapKeyFormat(YAML::LongKey, FmtScope::Local);
 
   PrepareNode(EmitterNodeType::Scalar);
 
   switch (strFormat) {
     case StringFormat::Plain:
-      m_stream << str;
+      m_stream.write(str, size);
       break;
     case StringFormat::SingleQuoted:
-      Utils::WriteSingleQuotedString(m_stream, str);
+      Utils::WriteSingleQuotedString(m_stream, str, size);
       break;
     case StringFormat::DoubleQuoted:
-      Utils::WriteDoubleQuotedString(m_stream, str, stringEscaping);
+      Utils::WriteDoubleQuotedString(m_stream, str, size, stringEscaping);
       break;
     case StringFormat::Literal:
-      Utils::WriteLiteralString(m_stream, str,
+      Utils::WriteLiteralString(m_stream, str, size,
                                 m_pState->CurIndent() + m_pState->GetIndent());
       break;
   }
@@ -752,6 +752,10 @@ Emitter& Emitter::Write(const std::string& str) {
   return *this;
 }
 
+Emitter& Emitter::Write(const std::string& str) {
+  return Write(str.data(), str.size());
+}
+
 std::size_t Emitter::GetFloatPrecision() const {
   return m_pState->GetFloatPrecision();
 }
@@ -865,7 +869,7 @@ Emitter& Emitter::Write(const _Alias& alias) {
 
   PrepareNode(EmitterNodeType::Scalar);
 
-  if (!Utils::WriteAlias(m_stream, alias.content)) {
+  if (!Utils::WriteAlias(m_stream, alias.content.data(), alias.content.size())) {
     m_pState->SetError(ErrorMsg::INVALID_ALIAS);
     return *this;
   }
@@ -888,7 +892,7 @@ Emitter& Emitter::Write(const _Anchor& anchor) {
 
   PrepareNode(EmitterNodeType::Property);
 
-  if (!Utils::WriteAnchor(m_stream, anchor.content)) {
+  if (!Utils::WriteAnchor(m_stream, anchor.content.data(), anchor.content.size())) {
     m_pState->SetError(ErrorMsg::INVALID_ANCHOR);
     return *this;
   }
@@ -937,7 +941,7 @@ Emitter& Emitter::Write(const _Comment& comment) {
 
   if (m_stream.col() > 0)
     m_stream << Indentation(m_pState->GetPreCommentIndent());
-  Utils::WriteComment(m_stream, comment.content,
+  Utils::WriteComment(m_stream, comment.content.data(), comment.content.size(),
                       m_pState->GetPostCommentIndent());
 
   m_pState->SetNonContent();

src/emitterutils.cpp

@@ -89,8 +89,8 @@ int Utf8BytesIndicated(char ch) {
 bool IsTrailingByte(char ch) { return (ch & 0xC0) == 0x80; }
 
 bool GetNextCodePointAndAdvance(int& codePoint,
-                                std::string::const_iterator& first,
-                                std::string::const_iterator last) {
+                                const char*& first,
+                                const char* last) {
   if (first == last)
     return false;
 
@@ -153,23 +153,23 @@ void WriteCodePoint(ostream_wrapper& out, int codePoint) {
   }
 }
 
-bool IsValidPlainScalar(const std::string& str, FlowType::value flowType,
+bool IsValidPlainScalar(const char* str, std::size_t size, FlowType::value flowType,
                         bool allowOnlyAscii) {
   // check against null
-  if (IsNullString(str)) {
+  if (IsNullString(str, size)) {
     return false;
   }
 
   // check the start
   const RegEx& start = (flowType == FlowType::Flow ? Exp::PlainScalarInFlow()
                                                    : Exp::PlainScalar());
-  if (!start.Matches(str)) {
+  if (!start.Matches(StringCharSource(str, size))) {
     return false;
   }
 
   // and check the end for plain whitespace (which can't be faithfully kept in a
   // plain scalar)
-  if (!str.empty() && *str.rbegin() == ' ') {
+  if (size != 0 && str[size - 1] == ' ') {
     return false;
   }
 
@@ -185,7 +185,7 @@ bool IsValidPlainScalar(const std::string& str, FlowType::value flowType,
   const RegEx& disallowed =
       flowType == FlowType::Flow ? disallowed_flow : disallowed_block;
 
-  StringCharSource buffer(str.c_str(), str.size());
+  StringCharSource buffer(str, size);
   while (buffer) {
     if (disallowed.Matches(buffer)) {
       return false;
@@ -199,22 +199,22 @@ bool IsValidPlainScalar(const std::string& str, FlowType::value flowType,
   return true;
 }
 
-bool IsValidSingleQuotedScalar(const std::string& str, bool escapeNonAscii) {
+bool IsValidSingleQuotedScalar(const char* str, std::size_t size, bool escapeNonAscii) {
   // TODO: check for non-printable characters?
-  return std::none_of(str.begin(), str.end(), [=](char ch) {
+  return std::none_of(str, str + size, [=](char ch) {
     return (escapeNonAscii && (0x80 <= static_cast<unsigned char>(ch))) ||
            (ch == '\n');
   });
 }
 
-bool IsValidLiteralScalar(const std::string& str, FlowType::value flowType,
+bool IsValidLiteralScalar(const char* str, std::size_t size, FlowType::value flowType,
                           bool escapeNonAscii) {
   if (flowType == FlowType::Flow) {
     return false;
   }
 
   // TODO: check for non-printable characters?
-  return std::none_of(str.begin(), str.end(), [=](char ch) {
+  return std::none_of(str, str + size, [=](char ch) {
     return (escapeNonAscii && (0x80 <= static_cast<unsigned char>(ch)));
   });
 }
@@ -254,10 +254,10 @@ void WriteDoubleQuoteEscapeSequence(ostream_wrapper& out, int codePoint, StringE
     out << hexDigits[(codePoint >> (4 * (digits - 1))) & 0xF];
 }
 
-bool WriteAliasName(ostream_wrapper& out, const std::string& str) {
+bool WriteAliasName(ostream_wrapper& out, const char* str, std::size_t size) {
   int codePoint;
-  for (std::string::const_iterator i = str.begin();
-       GetNextCodePointAndAdvance(codePoint, i, str.end());) {
+  for (const char* i = str;
+       GetNextCodePointAndAdvance(codePoint, i, str + size);) {
     if (!IsAnchorChar(codePoint)) {
       return false;
     }
@@ -268,25 +268,25 @@ bool WriteAliasName(ostream_wrapper& out, const std::string& str) {
 }
 }  // namespace
 
-StringFormat::value ComputeStringFormat(const std::string& str,
+StringFormat::value ComputeStringFormat(const char* str, std::size_t size,
                                         EMITTER_MANIP strFormat,
                                         FlowType::value flowType,
                                         bool escapeNonAscii) {
   switch (strFormat) {
     case Auto:
-      if (IsValidPlainScalar(str, flowType, escapeNonAscii)) {
+      if (IsValidPlainScalar(str, size, flowType, escapeNonAscii)) {
         return StringFormat::Plain;
       }
       return StringFormat::DoubleQuoted;
     case SingleQuoted:
-      if (IsValidSingleQuotedScalar(str, escapeNonAscii)) {
+      if (IsValidSingleQuotedScalar(str, size, escapeNonAscii)) {
         return StringFormat::SingleQuoted;
       }
       return StringFormat::DoubleQuoted;
     case DoubleQuoted:
       return StringFormat::DoubleQuoted;
     case Literal:
-      if (IsValidLiteralScalar(str, flowType, escapeNonAscii)) {
+      if (IsValidLiteralScalar(str, size, flowType, escapeNonAscii)) {
         return StringFormat::Literal;
       }
       return StringFormat::DoubleQuoted;
@@ -297,11 +297,11 @@ StringFormat::value ComputeStringFormat(const std::string& str,
   return StringFormat::DoubleQuoted;
 }
 
-bool WriteSingleQuotedString(ostream_wrapper& out, const std::string& str) {
+bool WriteSingleQuotedString(ostream_wrapper& out, const char* str, std::size_t size) {
   out << "'";
   int codePoint;
-  for (std::string::const_iterator i = str.begin();
-       GetNextCodePointAndAdvance(codePoint, i, str.end());) {
+  for (const char* i = str;
+       GetNextCodePointAndAdvance(codePoint, i, str + size);) {
     if (codePoint == '\n') {
       return false;  // We can't handle a new line and the attendant indentation
                      // yet
@@ -317,12 +317,12 @@ bool WriteSingleQuotedString(ostream_wrapper& out, const std::string& str) {
   return true;
 }
 
-bool WriteDoubleQuotedString(ostream_wrapper& out, const std::string& str,
+bool WriteDoubleQuotedString(ostream_wrapper& out, const char* str, std::size_t size,
                              StringEscaping::value stringEscaping) {
   out << "\"";
   int codePoint;
-  for (std::string::const_iterator i = str.begin();
-       GetNextCodePointAndAdvance(codePoint, i, str.end());) {
+  for (const char* i = str;
+       GetNextCodePointAndAdvance(codePoint, i, str + size);) {
     switch (codePoint) {
       case '\"':
         out << "\\\"";
@@ -364,12 +364,12 @@ bool WriteDoubleQuotedString(ostream_wrapper& out, const std::string& str,
   return true;
 }
 
-bool WriteLiteralString(ostream_wrapper& out, const std::string& str,
+bool WriteLiteralString(ostream_wrapper& out, const char* str, std::size_t size,
                         std::size_t indent) {
   out << "|\n";
   int codePoint;
-  for (std::string::const_iterator i = str.begin();
-       GetNextCodePointAndAdvance(codePoint, i, str.end());) {
+  for (const char* i = str;
+       GetNextCodePointAndAdvance(codePoint, i, str + size);) {
     if (codePoint == '\n') {
       out << "\n";
     } else {
@@ -407,14 +407,14 @@ bool WriteChar(ostream_wrapper& out, char ch, StringEscaping::value stringEscapi
   return true;
 }
 
-bool WriteComment(ostream_wrapper& out, const std::string& str,
+bool WriteComment(ostream_wrapper& out, const char* str, std::size_t size,
                   std::size_t postCommentIndent) {
   const std::size_t curIndent = out.col();
   out << "#" << Indentation(postCommentIndent);
   out.set_comment();
   int codePoint;
-  for (std::string::const_iterator i = str.begin();
-       GetNextCodePointAndAdvance(codePoint, i, str.end());) {
+  for (const char* i = str;
+       GetNextCodePointAndAdvance(codePoint, i, str + size);) {
     if (codePoint == '\n') {
       out << "\n"
           << IndentTo(curIndent) << "#" << Indentation(postCommentIndent);
@@ -426,14 +426,14 @@ bool WriteComment(ostream_wrapper& out, const std::string& str,
   return true;
 }
 
-bool WriteAlias(ostream_wrapper& out, const std::string& str) {
+bool WriteAlias(ostream_wrapper& out, const char* str, std::size_t size) {
   out << "*";
-  return WriteAliasName(out, str);
+  return WriteAliasName(out, str, size);
 }
 
-bool WriteAnchor(ostream_wrapper& out, const std::string& str) {
+bool WriteAnchor(ostream_wrapper& out, const char* str, std::size_t size) {
   out << "&";
-  return WriteAliasName(out, str);
+  return WriteAliasName(out, str, size);
 }
 
 bool WriteTag(ostream_wrapper& out, const std::string& str, bool verbatim) {
@@ -490,7 +490,8 @@ bool WriteTagWithPrefix(ostream_wrapper& out, const std::string& prefix,
 }
 
 bool WriteBinary(ostream_wrapper& out, const Binary& binary) {
-  WriteDoubleQuotedString(out, EncodeBase64(binary.data(), binary.size()),
+  std::string encoded = EncodeBase64(binary.data(), binary.size());
+  WriteDoubleQuotedString(out, encoded.data(), encoded.size(),
                           StringEscaping::None);
   return true;
 }

src/emitterutils.h

@@ -29,22 +29,22 @@ struct StringEscaping {
 };
 
 namespace Utils {
-StringFormat::value ComputeStringFormat(const std::string& str,
+StringFormat::value ComputeStringFormat(const char* str, std::size_t size,
                                         EMITTER_MANIP strFormat,
                                         FlowType::value flowType,
                                         bool escapeNonAscii);
 
-bool WriteSingleQuotedString(ostream_wrapper& out, const std::string& str);
-bool WriteDoubleQuotedString(ostream_wrapper& out, const std::string& str,
+bool WriteSingleQuotedString(ostream_wrapper& out, const char* str, std::size_t size);
+bool WriteDoubleQuotedString(ostream_wrapper& out, const char* str, std::size_t size,
                              StringEscaping::value stringEscaping);
-bool WriteLiteralString(ostream_wrapper& out, const std::string& str,
+bool WriteLiteralString(ostream_wrapper& out, const char* str, std::size_t size,
                         std::size_t indent);
 bool WriteChar(ostream_wrapper& out, char ch,
                StringEscaping::value stringEscapingStyle);
-bool WriteComment(ostream_wrapper& out, const std::string& str,
+bool WriteComment(ostream_wrapper& out, const char* str, std::size_t size,
                   std::size_t postCommentIndent);
-bool WriteAlias(ostream_wrapper& out, const std::string& str);
-bool WriteAnchor(ostream_wrapper& out, const std::string& str);
+bool WriteAlias(ostream_wrapper& out, const char* str, std::size_t size);
+bool WriteAnchor(ostream_wrapper& out, const char* str, std::size_t size);
 bool WriteTag(ostream_wrapper& out, const std::string& str, bool verbatim);
 bool WriteTagWithPrefix(ostream_wrapper& out, const std::string& prefix,
                         const std::string& tag);