ATreeModelIndex.h

#pragma once
 
#include <AUI/Common/AException.h>
#include <any>
#include <variant>

class ATreeModelIndex {
public:
   class Exception: public AException {
   public:
       using AException::AException;
   };

   explicit ATreeModelIndex(std::size_t row, std::size_t column, std::any userdata) noexcept:
       mRow(row),
       mColumn(column),
       mUserdata(std::move(userdata)) {}

   template<typename T>
   [[nodiscard]]
   T as() const {
       try {
           return std::any_cast<T>(mUserdata);
       } catch (...) {
           throw Exception("ATreeModelIndex::as any_cast failed (asked for {}, actually stored {})"_format(
               typeid(T).name(), mUserdata.type().name()));
       }
   }
 
   [[nodiscard]]
   bool hasValue() const noexcept {
       return mUserdata.has_value();
   }

   [[nodiscard]]
   std::size_t row() const {
       return mRow;
   }

   [[nodiscard]]
   std::size_t column() const {
       return mColumn;
   }

   static constexpr struct {} ROOT {};
 
private:
   std::size_t mRow;

   std::size_t mColumn;
   
   std::any mUserdata;
};

using ATreeModelIndexOrRoot = std::variant<ATreeModelIndex, decltype(ATreeModelIndex::ROOT)>;
 
// these allow the following expression:
// vertex == ATreeModelIndex::ROOT
 
inline bool operator==(const ATreeModelIndexOrRoot& lhs, const decltype(ATreeModelIndex::ROOT)&) {
   return !std::holds_alternative<ATreeModelIndex>(lhs);
}
 
inline bool operator!=(const ATreeModelIndexOrRoot& lhs, const decltype(ATreeModelIndex::ROOT)&) {
   return std::holds_alternative<ATreeModelIndex>(lhs);
}
 
// this allows the following expression:
// ATreeModelIndexOrRoot vertex = ...
// ATreeModelIndex index = *vertex
 
inline const ATreeModelIndex& operator*(const ATreeModelIndexOrRoot& v) {
   if (auto i = std::get_if<ATreeModelIndex>(&v)) {
       return *i;
   }
   throw ATreeModelIndex::Exception("ATreeModelIndexOrRoot holds root");
}

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