extractor_for.hpp

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/// \file jsonv/serialization/extractor_for.hpp
///
/// Copyright (c) 2015-2026 by Travis Gockel. All rights reserved.
///
/// This program is free software: you can redistribute it and/or modify it under the terms of the Apache License
/// as published by the Apache Software Foundation, either version 2 of the License, or (at your option) any later
/// version.
///
/// \author Travis Gockel (travis@gockelhut.com)
#pragma once
 
#include <jsonv/config.hpp>
#include <jsonv/serialization/extract.hpp>
 
#include <expected>
#include <new>
#include <utility>
 
namespace jsonv
{
 
/// \addtogroup Serialization
/// \{
 
/// An \c extractor for type \c T. This is a utility class which converts the `void*` used in the \c extractor
/// interface into the more-friendly \c T.
///
/// \see adapter_for
template <typename T>
class extractor_for :
        public extractor
{
public:
    /// \see extractor::get_type
    JSONV_NODISCARD
    virtual const std::type_info& get_type() const noexcept override
    {
        return typeid(T);
    }
 
    /// \see extractor::extract
    JSONV_NODISCARD
    virtual std::expected<void, ast_node_type>
    extract(extraction_context& context, reader& from, void* into) const override
    {
        if (auto created = create(context, from))
        {
            try
            {
                new(into) T(std::move(created).value());
            }
            catch (...)
            {
                // `create` succeeded, so the cursor is already one past the value this was built from. Moving it
                // into place is the last thing which can fail, and `T` is the caller's type; a loop recovering from
                // that failure must not step over the value a second time.
                context.note_value_consumed(from);
                throw;
            }
            return {};
        }
        else
        {
            return std::unexpected(created.error());
        }
    }
 
protected:
    /// Create an instance of \c T by reading \a from.
    ///
    /// \see adapter_for::create
    JSONV_NODISCARD
    virtual std::expected<T, ast_node_type> create(extraction_context& context, reader& from) const = 0;
};
 
/// \}
 
}