Improve LookaheadParser

Fix clang -Wswitch-enum warnings.
Made NextArrayValue() more robust—now handles error state correctly,
will enter error state if an unexpected state is reached.
Made separate states for each value type to simplify getters.
Simplified implementation of skipping arrays and objects.
Skipping an object now works whether you’ve retrieved the key or not.

example/lookaheadparser/lookaheadparser.cpp

@@ -19,15 +19,15 @@
 //
 // After calling EnterObject, you retrieve keys via NextObjectKey() and values via
 // the normal getters. When NextObjectKey() returns null, you have exited the
-// object, or you can call ExitObject() to skip to the end of the object
+// object, or you can call SkipObject() to skip to the end of the object
 // immediately. If you fetch the entire object (i.e. NextObjectKey() returned  null),
-// you should not call ExitObject().
+// you should not call SkipObject().
 //
 // After calling EnterArray(), you must alternate between calling NextArrayValue()
 // to see if the array has more data, and then retrieving values via the normal
-// getters. You can call ExitArray() to skip to the end of the array immediately.
+// getters. You can call SkipArray() to skip to the end of the array immediately.
 // If you fetch the entire array (i.e. NextArrayValue() returned null),
-// you should not call ExitArray().
+// you should not call SkipArray().
 //
 // This parser uses in-situ strings, so the JSON buffer will be altered during the
 // parse.
@@ -37,15 +37,15 @@ using namespace rapidjson;
 
 class LookaheadParserHandler {
 public:
-    bool Null() { st_ = kHasValue; v_.SetNull(); return true; }
-    bool Bool(bool b) { st_ = kHasValue; v_.SetBool(b); return true; }
-    bool Int(int i) { st_ = kHasValue; v_.SetInt(i); return true; }
-    bool Uint(unsigned u) { st_ = kHasValue; v_.SetUint(u); return true; }
-    bool Int64(int64_t i) { st_ = kHasValue; v_.SetInt64(i); return true; }
-    bool Uint64(uint64_t u) { st_ = kHasValue; v_.SetUint64(u); return true; }
-    bool Double(double d) { st_ = kHasValue; v_.SetDouble(d); return true; }
+    bool Null() { st_ = kHasNull; v_.SetNull(); return true; }
+    bool Bool(bool b) { st_ = kHasBool; v_.SetBool(b); return true; }
+    bool Int(int i) { st_ = kHasNumber; v_.SetInt(i); return true; }
+    bool Uint(unsigned u) { st_ = kHasNumber; v_.SetUint(u); return true; }
+    bool Int64(int64_t i) { st_ = kHasNumber; v_.SetInt64(i); return true; }
+    bool Uint64(uint64_t u) { st_ = kHasNumber; v_.SetUint64(u); return true; }
+    bool Double(double d) { st_ = kHasNumber; v_.SetDouble(d); return true; }
     bool RawNumber(const char*, SizeType, bool) { return false; }
-    bool String(const char* str, SizeType length, bool) { st_ = kHasValue; v_.SetString(str, length); return true; }
+    bool String(const char* str, SizeType length, bool) { st_ = kHasString; v_.SetString(str, length); return true; }
     bool StartObject() { st_ = kEnteringObject; return true; }
     bool Key(const char* str, SizeType length, bool) { st_ = kHasKey; v_.SetString(str, length); return true; }
     bool EndObject(SizeType) { st_ = kExitingObject; return true; }
@@ -59,7 +59,10 @@ protected:
 protected:
     enum LookaheadParsingState {
         kError,
-        kHasValue,
+        kHasNull,
+        kHasBool,
+        kHasNumber,
+        kHasString,
         kHasKey,
         kEnteringObject,
         kExitingObject,
@@ -93,10 +96,8 @@ class LookaheadParser : protected LookaheadParserHandler {
 public:
     LookaheadParser(char* str) : LookaheadParserHandler(str) {}
     
-    void EnterObject();
-    void EnterArray();
-    void ExitObject();
-    void ExitArray();
+    bool EnterObject();
+    bool EnterArray();
     const char* NextObjectKey();
     bool NextArrayValue();
     int GetInt();
@@ -105,70 +106,87 @@ public:
     bool GetBool();
     void GetNull();
 
+    void SkipObject();
+    void SkipArray();
     void SkipValue();
     Value* PeekValue();
     int PeekType(); // returns a rapidjson::Type, or -1 for no value (at end of object/array)
     
     bool IsValid() { return st_ != kError; }
+    
+protected:
+    void SkipOut(int depth);
 };
 
-void LookaheadParser::EnterObject() {
+bool LookaheadParser::EnterObject() {
     if (st_ != kEnteringObject) {
         st_  = kError;
-        return;
+        return false;
     }
     
     ParseNext();
+    return true;
 }
 
-void LookaheadParser::EnterArray() {
+bool LookaheadParser::EnterArray() {
     if (st_ != kEnteringArray) {
         st_  = kError;
-        return;
+        return false;
     }
     
     ParseNext();
-}
-
-void LookaheadParser::ExitObject() {
-    while (NextObjectKey()) {
-        SkipValue();
-    }
-}
-
-void LookaheadParser::ExitArray() {
-    while (NextArrayValue()) {
-        SkipValue();
-    }
+    return true;
 }
 
 const char* LookaheadParser::NextObjectKey() {
-    if (st_ == kExitingObject) {
-        ParseNext();
-        return 0;
-    }
-
-    if (st_ != kHasKey || !v_.IsString()) {
-        st_ = kError;
-        return 0;
+    switch (st_) {
+        case kHasKey: {
+            const char* result = v_.GetString();
+            ParseNext();
+            return result;
+        }
+            
+        case kExitingObject:
+            ParseNext();
+            return 0;
+            
+        case kError:
+        case kHasNull:
+        case kHasBool:
+        case kHasNumber:
+        case kHasString:
+        case kEnteringObject:
+        case kEnteringArray:
+        case kExitingArray:
+            st_ = kError;
+            return 0;
     }
-    
-    const char* result = v_.GetString();
-    ParseNext();
-    return result;
 }
 
 bool LookaheadParser::NextArrayValue() {
-    if (st_ == kExitingArray) {
-        ParseNext();
-        return false;
+    switch (st_) {
+        case kExitingArray:
+            ParseNext();
+            return false;
+            
+        case kError:
+        case kExitingObject:
+        case kHasKey:
+            st_ = kError;
+            return false;
+            
+        case kHasNull:
+        case kHasBool:
+        case kHasNumber:
+        case kHasString:
+        case kEnteringObject:
+        case kEnteringArray:
+            return true;
     }
-    
-    return true;
 }
 
 int LookaheadParser::GetInt() {
-    if (st_ != kHasValue || !v_.IsInt()) {
+    if (st_ != kHasNumber || !v_.IsInt()) {
         st_ = kError;
         return 0;
     }
@@ -179,7 +197,7 @@ int LookaheadParser::GetInt() {
 }
 
 double LookaheadParser::GetDouble() {
-    if (st_ != kHasValue || !v_.IsNumber()) {
+    if (st_ != kHasNumber || !v_.IsNumber()) {
         st_  = kError;
         return 0.;
     }
@@ -190,7 +208,7 @@ double LookaheadParser::GetDouble() {
 }
 
 bool LookaheadParser::GetBool() {
-    if (st_ != kHasValue || !v_.IsBool()) {
+    if (st_ != kHasBool) {
         st_  = kError;
         return false;
     }
@@ -201,7 +219,7 @@ bool LookaheadParser::GetBool() {
 }
 
 void LookaheadParser::GetNull() {
-    if (st_ != kHasValue || !v_.IsNull()) {
+    if (st_ != kHasNull) {
         st_  = kError;
         return;
     }
@@ -210,7 +228,7 @@ void LookaheadParser::GetNull() {
 }
 
 const char* LookaheadParser::GetString() {
-    if (st_ != kHasValue || !v_.IsString()) {
+    if (st_ != kHasString) {
         st_  = kError;
         return 0;
     }
@@ -220,8 +238,7 @@ const char* LookaheadParser::GetString() {
     return result;
 }
 
-void LookaheadParser::SkipValue() {
-    int depth = 0;
+void LookaheadParser::SkipOut(int depth) {
     do {
         switch (st_) {
             case kEnteringArray:
@@ -237,8 +254,11 @@ void LookaheadParser::SkipValue() {
             case kError:
                 return;
                 
-            case kHasKey:
-            case kHasValue:
+		    case kHasNull:
+		    case kHasBool:
+		    case kHasNumber:
+		    case kHasString:
+		    case kHasKey:
                 break;
         }
         ParseNext();
@@ -246,8 +266,20 @@ void LookaheadParser::SkipValue() {
     while (depth > 0);
 }
 
+void LookaheadParser::SkipValue() {
+    SkipOut(0);
+}
+
+void LookaheadParser::SkipArray() {
+    SkipOut(1);
+}
+
+void LookaheadParser::SkipObject() {
+    SkipOut(1);
+}
+
 Value* LookaheadParser::PeekValue() {
-    if (st_ == kHasValue || st_ == kHasKey) {
+    if (st_ >= kHasNull && st_ <= kHasKey) {
         return &v_;
     }
     
@@ -256,7 +288,10 @@ Value* LookaheadParser::PeekValue() {
 
 int LookaheadParser::PeekType() {
     switch (st_) {
-        case kHasValue:
+        case kHasNull:
+        case kHasBool:
+        case kHasNumber:
+        case kHasString:
         case kHasKey:
             return v_.GetType();
         
@@ -269,7 +304,6 @@ int LookaheadParser::PeekType() {
         case kExitingArray:
         case kExitingObject:
         case kError:
-        default:
             return -1;
     }
 }
@@ -325,7 +359,7 @@ int main() {
                     cout << r.GetString() << " ";
                 }
                 else {
-                    r.ExitArray();
+                    r.SkipArray();
                     break;
                 }
             }