function_adapter.hpp

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/// \file jsonv/serialization/function_adapter.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 "adapter_for.hpp"
 
#include <expected>
#include <utility>
 
namespace jsonv
{
 
/// \addtogroup Serialization
/// \{
 
template <typename T, typename FExtract, typename FToJson>
class function_adapter :
        public adapter_for<T>
{
public:
    template <typename FUExtract, typename FUToJson>
    explicit function_adapter(FUExtract&& extract_, FUToJson&& to_json_) :
            _extract(std::forward<FUExtract>(extract_)),
            _to_json(std::forward<FUToJson>(to_json_))
    { }
 
protected:
    JSONV_NODISCARD
    virtual std::expected<T, ast_node_type> create(extraction_context& context, reader& from) const override
    {
        return detail::invoke_extract<T>(_extract, context, from);
    }
 
    JSONV_NODISCARD
    virtual value to_json(const serialization_context& context, const T& from) const override
    {
        return to_json_impl(_to_json, context, from);
    }
 
private:
    template <typename FUToJson>
    static auto to_json_impl(const FUToJson& func, const serialization_context& context, const T& from)
            -> decltype(func(context, from))
    {
        return func(context, from);
    }
 
    template <typename FUToJson, typename = void>
    static auto to_json_impl(const FUToJson& func, const serialization_context&, const T& from)
            -> decltype(func(from))
    {
        return func(from);
    }
 
private:
    FExtract _extract;
    FToJson  _to_json;
};
 
/// Create an \c adapter from \a extract and \a to_json_, deducing the adapted type from what \a extract returns.
template <typename FExtract, typename FToJson>
JSONV_NODISCARD
auto make_adapter(FExtract extract, FToJson to_json_)
    -> function_adapter<detail::extract_function_result_t<FExtract>, FExtract, FToJson>
{
    return function_adapter<detail::extract_function_result_t<FExtract>, FExtract, FToJson>
            (std::move(extract), std::move(to_json_));
}
 
/// \}
 
}