Refactor.

include/xgboost/json.h

@@ -271,8 +271,8 @@ struct StringView {
   size_t size() const { return size_; }  // NOLINT
   // Copies a portion of string.  Since we don't have std::from_chars and friends here, so
   // copying substring is necessary for appending `\0`.  It's not too bad since string by
-  // default has small vector optimization, for numeric value where max length is 17, the
-  // optimization should be enabled by most if not all modern compiler.
+  // default has small vector optimization, which is enabled by most if not all modern
+  // compilers for numeric values.
   std::string substr(size_t beg, size_t n) const {  // NOLINT
     CHECK_LE(beg, size_);
     return std::string {str_ + beg, n < (size_ - beg) ? n : (size_ - beg)};

include/xgboost/json_io.h

@@ -15,6 +15,18 @@
 #include <locale>
 
 namespace xgboost {
+
+template <typename Allocator>
+class FixedPrecisionStreamContainer : public std::basic_stringstream<
+  char, std::char_traits<char>, Allocator> {
+ public:
+  FixedPrecisionStreamContainer() {
+    this->precision(std::numeric_limits<Number::Float>::max_digits10);
+  }
+};
+
+using FixedPrecisionStream = FixedPrecisionStreamContainer<std::allocator<char>>;
+
 class JsonReader {
  protected:
   size_t constexpr static kMaxNumLength =
@@ -117,16 +129,50 @@ class JsonReader {
   }
 };
 
-template <typename Allocator>
-class FixedPrecisionStreamContainer : public std::basic_stringstream<
-  char, std::char_traits<char>, Allocator> {
+class JsonWriter {
+  static constexpr size_t kIndentSize = 2;
+  FixedPrecisionStream convertor_;
+
+  size_t n_spaces_;
+  std::ostream* stream_;
+  bool pretty_;
+
  public:
-  FixedPrecisionStreamContainer() {
-    this->precision(std::numeric_limits<Number::Float>::max_digits10);
+  JsonWriter(std::ostream* stream, bool pretty) :
+      n_spaces_{0}, stream_{stream}, pretty_{pretty} {}
+
+  virtual ~JsonWriter() = default;
+
+  void NewLine() {
+    if (pretty_) {
+      *stream_ << u8"\n" << std::string(n_spaces_, ' ');
+    }
   }
-};
 
-using FixedPrecisionStream = FixedPrecisionStreamContainer<std::allocator<char>>;
+  void BeginIndent() {
+    n_spaces_ += kIndentSize;
+  }
+  void EndIndent() {
+    n_spaces_ -= kIndentSize;
+  }
+
+  void Write(std::string str) {
+    *stream_ << str;
+  }
+  void Write(StringView str) {
+    stream_->write(str.c_str(), str.size());
+  }
+
+  void Save(Json json);
+
+  virtual void Visit(JsonArray  const* arr);
+  virtual void Visit(JsonObject const* obj);
+  virtual void Visit(JsonNumber const* num);
+  virtual void Visit(JsonRaw    const* raw);
+  virtual void Visit(JsonNull   const* null);
+  virtual void Visit(JsonString const* str);
+  virtual void Visit(JsonBoolean const* boolean);
+};
 }      // namespace xgboost
 
 #endif  // XGBOOST_JSON_IO_H_

src/common/json.cc

@@ -10,51 +10,6 @@
 
 namespace xgboost {
 
-class JsonWriter {
-  static constexpr size_t kIndentSize = 2;
-  FixedPrecisionStream convertor_;
-
-  size_t n_spaces_;
-  std::ostream* stream_;
-  bool pretty_;
-
- public:
-  JsonWriter(std::ostream* stream, bool pretty) :
-      n_spaces_{0}, stream_{stream}, pretty_{pretty} {}
-
-  virtual ~JsonWriter() = default;
-
-  void NewLine() {
-    if (pretty_) {
-      *stream_ << u8"\n" << std::string(n_spaces_, ' ');
-    }
-  }
-
-  void BeginIndent() {
-    n_spaces_ += kIndentSize;
-  }
-  void EndIndent() {
-    n_spaces_ -= kIndentSize;
-  }
-
-  void Write(std::string str) {
-    *stream_ << str;
-  }
-  void Write(StringView str) {
-    stream_->write(str.c_str(), str.size());
-  }
-
-  void Save(Json json);
-
-  virtual void Visit(JsonArray  const* arr);
-  virtual void Visit(JsonObject const* obj);
-  virtual void Visit(JsonNumber const* num);
-  virtual void Visit(JsonRaw    const* raw);
-  virtual void Visit(JsonNull   const* null);
-  virtual void Visit(JsonString const* str);
-  virtual void Visit(JsonBoolean const* boolean);
-};
-
 void JsonWriter::Save(Json json) {
   json.ptr_->Save(this);
 }
@@ -558,12 +513,9 @@ Json JsonReader::ParseObject() {
 Json JsonReader::ParseNumber() {
   std::string substr = raw_str_.substr(cursor_.Pos(), kMaxNumLength);
   size_t pos = 0;
+
   Number::Float number{0};
-  if (std::is_same<Number::Float, float>::value) {
-    number = std::stof(substr, &pos);
-  } else {
-    number = std::stod(substr, &pos);
-  }
+  number = std::stof(substr, &pos);
   for (size_t i = 0; i < pos; ++i) {
     GetNextChar();
   }
@@ -597,25 +549,28 @@ Json JsonReader::ParseBoolean() {
   return Json{JsonBoolean{result}};
 }
 
-class GlobalUtf8Locale {
+// This is an ad-hoc solution for writing numeric value in standard way.  We need to add
+// something locale independent way of writing stream.
+// FIXME(trivialfis): Remove this.
+class GlobalCLocale {
   std::locale ori_;
 
  public:
-  GlobalUtf8Locale() : ori_{std::locale()} {
+  GlobalCLocale() : ori_{std::locale()} {
     std::string const name {"C"};
     try {
       std::locale::global(std::locale(name.c_str()));
     } catch (std::runtime_error const& e) {
       LOG(FATAL) << "Failed to set locale: " << name;
     }
   }
-  ~GlobalUtf8Locale() {
+  ~GlobalCLocale() {
     std::locale::global(ori_);
   }
 };
 
 Json Json::Load(StringView str, bool ignore_specialization) {
-  GlobalUtf8Locale guard;
+  GlobalCLocale guard;
   LOG(WARNING) << "Json serialization is still experimental."
       "  Output schema is subject to change in the future.";
   JsonReader reader(str, ignore_specialization);
@@ -628,7 +583,7 @@ Json Json::Load(StringView str, bool ignore_specialization) {
 }
 
 Json Json::Load(JsonReader* reader) {
-  GlobalUtf8Locale guard;
+  GlobalCLocale guard;
   common::Timer t;
   t.Start();
   Json json{reader->Load()};
@@ -638,7 +593,7 @@ Json Json::Load(JsonReader* reader) {
 }
 
 void Json::Dump(Json json, std::ostream *stream, bool pretty) {
-  GlobalUtf8Locale guard;
+  GlobalCLocale guard;
   LOG(WARNING) << "Json serialization is still experimental."
       "  Output schema is subject to change in the future.";
   JsonWriter writer(stream, true);