Unable to locate 'to_json()' and 'from_json()' methods in the same namespace

[federicoorta]

I am trying out this nice library and to learn how to use it, after running the examples, I started working on a very small example on my own.

Here it is:

namespace defe {
    class Item {

    public:
        { constructor/destructor }

        { getters&setters }

        void to_json(json& j, const defe::Item& item) {
            j = json{{"name",                item.name},
                     {"type",                item.type},
                     {"lengthInByte",        item.lengthInByte},
                     {"elementDescriptions", item.elementDescriptions}};
        }

        void from_json(const json& j, defe::Item& item) {
            item.name = j.at("name").get<std::string>();
            item.type = j.at("type").get<std::string>();
            item.lengthInByte = j.at("lengthInByte").get<unsigned short int>();
            item.elementDescriptions = j.at("elementDescriptions").get<std::vector<std::vector<std::string>>>();
        }

    private:
        std::string name;
        std::string type;
        unsigned short int lengthInByte;
        std::vector<std::vector<std::string>> elementDescriptions;
    };

    class CategoryDescription {

    public:
        { constructor/destructor }

        { getters&setters }

        void to_json(json& j, const defe::CategoryDescription& catDesc) {
            j = json{{"item", catDesc.item}};
        }

        void from_json(const json& j, defe::CategoryDescription& catDesc) {
            catDesc.item = j.at("itemCollection").get<std::vector<defe::Item>>();
        }

    private:
        std::vector<defe::Item> items;
    };
}

I compiled it twice: the first one, just with the Item class and it has been successful.
Then, I added the CategoryDescription class, where I have a vector of Item instances.
GCC 7.2.0 on Ubuntu 17.10

When I try to compile the complete version (you find here), the compilation fails with the following error:

error: static assertion failed: could not find from_json() method in T's namespace
         static_assert(sizeof(BasicJsonType) == 0

I learned from the docs and from other issue answers that such an error tells that the to_json() and from_json() methods have not been located, isn't it?
So my question is: am I required to write a specialization of adl_serializer, even if both classes belongs to the same namespace?

I am a bit confused, I apologize for that. It might be that I am mixing up two different problems.
But I am sure to have defined the two classes in the right order (ref. issue 561). The latter class (CategoryDescription) is making use of the former class (Item).

Thank you for your help :)
If I have missed something, feel free to ask further details.

Best Regards

[theodelrieu]

No worries, you don't have to write a serializer, your issue is that the to_json/from_json functions MUST BE free functions (i.e. outside of your class).

Moving them outside should fix your problem.

[federicoorta]

Oh.. just that? :)
I don't know why I thought that those methods should have been member functions..

I will try again later today and I will come back to report the result.
Thank you!

[federicoorta]

Thank you, Théo! All is working! 👍

Now it's time to go further with this great library! Thank you, Niels too! :)