Types.h

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/** @noop License Comment
 *  @file
 *  @copyright
 *  This Source Code is subject to the terms of the Mozilla Public License, v2.0.
 *  If a copy of the MPL was not distributed with this file You can obtain one at
 *  https://mozilla.org/MPL/2.0/
 *  
 *  @author David Mórász
 *  @date 2025
 */
 
#pragma once
 
#include <string>
 
#include "CoreMinimal.h"
#include "Mcro/TypeName.h"
#include "Mcro/Templates.h"
 
/** C++ native static reflection utilities, not to be confused with reflection of UObjects */
namespace Mcro::Types
{
    using namespace Mcro::TypeName;
    using namespace Mcro::Templates;
    
    class IHaveType;
 
    template <typename T>
    concept CHasTypeName = CDerivedFrom<T, IHaveType>;
 
    /**
     *  A barebones base class for types which may store their type-name as a string
     *
     *  @todo
     *  C++ 26 has promising proposal for static value-based reflection, which can gather metadata from classes
     *  or even emit them. The best summary I found so far is a stack-overflow answer https://stackoverflow.com/a/77477029
     *  Once that's available we can gather base classes in compile time, and do dynamic casting of objects without
     *  the need for intrusive extra syntax, or extra work at construction.
     *  Currently GCC's `__bases` would be perfect for the job, but other popular compilers don't have similar intrinsics.
     */
    class IHaveType : public TSharedFromThis<IHaveType>
    {
    public:
        virtual ~IHaveType() = default;
        
    protected:
        FName TypeName;
 
        /** This function needs to be called on top level derived type for runtime reflection to work */
        template <typename Self>
        void SetType(this Self&& self)
        {
            self.TypeName = TTypeFName<Self>;
        }
        
    public:
        template <typename Self>
        using SelfRef = TSharedRef<std::decay_t<Self>>;
 
        /** Fluent API for setting tpye for deferred initialization (for example in factory functions) */
        template <typename Self>
        SelfRef<Self> WithType(this Self&& self)
        {
            self.SetType();
            return SharedThis(&self);
        }
 
        FORCEINLINE FName const& GetType() const { return TypeName; }
 
        /**
         *  Very simple dynamic casting of this object to a derived top-level type.
         *
         *  @tparam Derived
         *  Only return the desired type when the current object is exactly that type, and doesn't have deeper
         *  inheritance. Proper dynamic casting regarding the entire inheritance tree still without RTTI will come once
         *  proposed C++26 value-typed reflection becomes available.
         *
         *  @return  Object cast to desired type when that's possible (see `Derived`) or nullptr;
         */
        template <typename Derived, typename Self>
        TSharedPtr<Derived> AsExactly(this Self&& self)
        {
            if constexpr (CDerivedFrom<Derived, Self>)
                if (self.TypeName == TTypeFName<Derived>)
                    return StaticCastSharedPtr<Derived>(
                        SharedThis(AsMutablePtr(&self)).ToSharedPtr()
                    );
            return {};
        }
    };
}