Creating instances of opaque types from .json file data

[TerensTare]

Hello there. I am using SDL2 together with nlohmann::json (this library), and I wanted to load some SDL_Texture-s from a .json file, which contains the names of some image files. The problem is that SDL_Texture is an opaque data type (the struct's definition is on a C source(.c) file rather than on a header(.h) file). However, SDL2 provides some factory functions which need a filename and a renderer pointer (not related to the question). I already read the examples section on README.md, but I can't find anything that can help me.

[nlohmann]

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[TerensTare]

Sorry for not giving enough information.
To start with, I am using vcpkg's latest updated port of nlohmann::json with the x64-windows triplet. The OS is Windows 10 with the Visual Studio 2019 C++ compiler. I am not having any compilation or even any problem with code not behaving correctly.
The problem I have is that I want to load an image to the screen, and get the name of the image file from a .json file.
ex.:

{
    "width": 100,
    "height": 100,
    "file": "myImage.png"
}

I use SDL2 (written in C) for handling graphics. It provides a SDL_Texture structure for handling images/textures. But SDL_Texture is an opaque type (meaning that on the header file it is just typedef struct SDL_Texture SDL_Texture;, and the body of the structure is defined on a .c file), and SDL_Image provides a function named IMG_LoadTexture for creating SDL_Texture* for you (the user). I can easily parse/extract width and height from the .json file, but I am not sure about the way I should specialise nlohmann::adl_serializer for SDL_Texture.

[nlohmann]

Did you try to define a to_json/from_json function for SDL_Texture?

[TerensTare]

As a matter of fact, I only tried to define an specialisation of nlohmann::adl_serializer<SDL_Texture> by following the examples section on README.md. At first I didn't fully understand how basic_json and its members worked.
I used to write sth like:

namespace nlohmann {
template<> struct adl_serializer<SDL_Texture> {
static void from_json(nlohmann::json const& j, SDL_Texture* tex) {
j.at("file").get_to(tex): // I thought using get_to was mandatory, that's why I couldn't figure out a solution
}
};
}

But after I walked through the whole examples, checked the return types of basic_json member functions and experimented a bit with them, I came up with this solution. So basically I wrote a TextureManager class. It's only purpose is to handle the lifetime of SDL_Texture-s for the user. I added a from_json function defined like this:

SDL_Texture* TextureManager::from_json(SDL_Renderer* ren, nlohmann::json const& j)
{
char const* file{j.at("file")};
SDL_Texture* ret = IMG_LoadTexture(ren, file);
}

Now I use that function to load SDL_Texture-s for me. Thank you for everything, your help and the examples were invaluable for me.