____                         ___________          _________  __                            __
    |    |  ______  ____    ____  \__    ___/  ____   /   _____/_/  |_ _______  __ __   ____  _/  |_
    |    | /  ___/ /  _ \  /    \   |    |    /  _ \  \_____  \ \   __\\_  __ \|  |  \_/ ___\ \   __\
/\__|    | \___ \ (  <_> )|   |  \  |    |   (  <_> ) /        \ |  |   |  | \/|  |  /\  \___  |  |
\________|/____  > \____/ |___|  /  |____|    \____/ /_______  / |__|   |__|   |____/  \___  > |__|
               \/              \/                            \/                            \/

Code generator for generating C++ type definitions from JSON-schema definitions

Following types are currently supported:

1. Simple type aliases
2. Array (vector) type aliases
3. Enums
4. Variant type aliases
5. Structures
6. Extended variants (special case of a struct, see below)

Examples

1. Defining a simple type alias

JSON schema definition

 "MyInt" : {
     "type" "integer"
 }

Generated C++ code

using MyInt = int32_t;

2. Defining an array alias

JSON schema definition

 "MyIntArray" : {
     "type" "array",
     "items": {
          "type" : "integer"
      }
 }

Generated C++ code

using MyIntArray = std::vector<int32_t>;

NOTE:

• Arrays are implemented as vectors as they are generally more convenient.

3. Defining an enum

JSON schema definition

 "MyEnum" : {
     "enum": [
          "zero",
          "one",
          "two",
          "three",
      ]
 }

Generated C++ code

enum class MyEnum
{
    zero = 0,
    one = 1,
    two = 2,
    three = 3,
};

4. Defining a variant alias

JSON schema definition

 "MyVariant" : {
     "oneOf": [
         {
             "type" : "integer"
         },
         {
             "type" : "string"
         },
         {
             "type" : "array",
             "items" : {
                 "type": "boolean"
             }
         },
     ]
 }

Generated C++ code

using MyVariant = std::variant<int32_t, std::string, std::vector<bool>>;

5. Defining a C++ Structure

JSON schema definition

 "MyStruct" : {
     "type": "object",
     "properties": {
         "name": {
             "type" : "string"
         },
         "age": {
             "type" : "integer"
         },
         "scores": {
             "type" : "array",
             "items" : {
                 "type": "integer"
             }
         },
     }
 }

Generated C++ code

struct MyStruct
{
    std::string name;
    int32_t age;
    std::vector<int32_t> scores;
};

NOTE:

• In addition to generating the struct members, the tool also generates two helper functions to Serialize/Deserialize the object to/from json formatted string.

6. Defining an extended variants

JSON schema definition

 "MyExtendedVariant" : {
     "type": "object",
     "@meta:cpp_type": "extended_variant",
     "properties": {
         "type": {
             "enum": ["int", "str", "array"]
         },
         "content": {
             "oneOf" : [
                 {
                     "type": "integer"
                 },
                 {
                     "type": "string"
                 },
                 {
                     "type": "array",
                     "items": {
                         "type": "number"
                     }
                 },
             ]
         }
     }
 }

Generated C++ code

struct MyStruct : std::variant<std::monostate, int32_t, std::string, std::vector<float>>
{
    enum class Type : int32_t
    {
        int = 1,
        str = 2,
        array = 3,
    };

    template <Type MemberType, typename T>
    void SetAs(T value) { emplace<static_cast<int32_t>(MemberType)>(value); }

    template <Type MemberType>
    [[nodiscard]] auto& GetAs() { return std::get<static_cast<int32_t>(MemberType)>(*this); }

    template <Type MemberType>
    [[nodiscard]] auto const& GetAs() const { return std::get<static_cast<int32_t>(MemberType)>(*this); }
};

NOTE:

• This is a struct that extend std::variant with defined list of variant member types.
• This is introduced for convenience when using variants whose members need to be accessed via an enum.
• This type may not be needed in simple use cases.
• Custom attribute @meta:cpp_type is used to distinguish this from a struct definition.
• std::monostate type is implicitly added as the first variant member to make the variant default constructable without a significant overhead.