How to assign json value to enum type in C++?

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C++

I have assigned string, integer and enum value to json object.
I need to get back the original value from jso object.
I am getting problem when converting json value to enum type.

enum Topic{ BOOK, PEN, PENCIL};
Json::Value record;

record["hello"] = "world";
record["number"] = 2;
record["topic"] = Topic; // no error

std::string str = record["hello"].asString();
int val = record["number"].asInt();

enum TopicType = record["topic"]; // Error

What I have tried:

enum Topic{ BOOK, PEN, PENCIL};
Json::Value record;

record["hello"] = "world";
record["number"] = 2;
record["topic"] = Topic; // no error

std::string str = record["hello"].asString();
int val = record["number"].asInt();

enum TopicType = record["topic"]; // Error