Boost option: how to simulate JSON?

Question

I am trying to parse a JSON string using a Boost Spirit object, storing a JSON object in recursive data structures:

Value <== [null, bool, long, double, std::string, Array, Object]; Array <== [Value, Value, Value, ...]; Object <== ["name1": Value, "name2": Value, ...]; 

And here is my code:

 #include <map> #include <vector> #include <string> #include <boost/variant.hpp> #include <boost/shared_array.hpp> #include <boost/shared_ptr.hpp> struct JsonNull {}; struct JsonValue; typedef std::map<std::string, JsonValue *> JsonObject; typedef std::vector<JsonValue *> JsonArray; struct JsonValue : boost::variant<JsonNull, bool, long, double, std::string, JsonArray, JsonObject> { }; JsonValue aval = JsonObject(); 

When compiling, I get an error:

 Error C2440: 'initializing' : cannot convert from 'std::map<_Kty,_Ty>' to 'JsonValue' 

Also, how to use JsonValue for JsonObject safely? When I try to do:

 boost::get<JsonObject>(aval) = JsonObject(); 

This gets a runtime exception / fatal failure.

Any help is greatly appreciated.

EDIT:

Following @Nicol's advice, I came out with the following code:

 struct JsonNull {}; struct JsonValue; typedef std::map<std::string, JsonValue *> JsonObject; typedef std::vector<JsonValue *> JsonArray; typedef boost::variant< JsonNull, bool, long, double, std::string, JsonObject, JsonArray, boost::recursive_wrapper<JsonValue> > JsonDataValue; struct JsonValue { JsonDataValue data; }; 

I can work with JsonObject and JsonArray as easily as this:

 JsonValue *pJsonVal = new JsonValue(); boost::get<JsonObject>(pCurrVal->data).insert( std::pair<std::string, JsonValue *>("key", pJsonVal) ); boost::get<JsonArray>(pCurrVal->data).push_back(pJsonVal); 

Just post it so everyone can benefit from it.

Answer 1

You must use a recursive shell (and you should not be pulled from boost::variant ):

 struct JsonValue; typedef boost::variant</*types*/, boost::recursive_wrapper<JsonValue> > JsonDataValue; struct JsonValue { JsonDataValue value; }; 

In order for Boost.Spirit to take JsonValue, you will need to write one of these Fusion adapters in order to adapt the type of the raw option to the structure.

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Also, how to use JsonValue for JsonObject safely? When I try to do:

This is not how options work. If you want to set them to a value, just set them like any other value:

 JsonValue val; val.value = JsonValue();