monero/contrib/epee/include/serialization/wire/field.h

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#pragma once

#include <functional>
#include <utility>

#include "serialization/wire/traits.h"

//! A required field has the same key name and C/C++ name
#define WIRE_FIELD(name)                                \
  ::wire::field( #name , std::ref( self . name ))

//! A required field has the same key name and C/C++ name AND is cheap to copy (faster output).
#define WIRE_FIELD_COPY(name)                   \
  ::wire::field( #name , self . name )

//! The optional field has the same key name and C/C++ name
#define WIRE_OPTIONAL_FIELD(name)                               \
  ::wire::optional_field( #name , std::ref( self . name ))

namespace wire
{
  /*! Links `name` to a `value` for object serialization.

    `value_type` is `T` with optional `std::reference_wrapper` removed.
    `value_type` needs a `read_bytes` function when parsing with a
    `wire::reader` - see `read.h` for more info. `value_type` needs a
    `write_bytes` function when writing with a `wire::writer` - see `write.h`
    for more info.

    Any `value_type` where `is_optional_on_empty<value_type> == true`, will
    automatically be converted to an optional field iff `value_type` has an
    `empty()` method that returns `true`. The old output engine omitted fields
    when an array was empty, and the standard input macro would ignore the
    `false` return for the missing field. For compability reasons, the
    input/output engine here matches that behavior. See `wrapper/array.h` to
    enforce a required field even when the array is empty or specialize the
    `is_optional_on_empty` trait. Only new fields should use this behavior.

    Additional concept requirements for `value_type` when `Required == false`:
      * must have an `operator*()` function.
      * must have a conversion to bool function that returns true when
        `operator*()` is safe to call (and implicitly when the associated field
        should be written as opposed to skipped/omitted).
    Additional concept requirements for `value_type` when `Required == false`
    when reading:
      * must have an `emplace()` method that ensures `operator*()` is safe to call.
      * must have a `reset()` method to indicate a field was skipped/omitted.

    If a standard type needs custom serialization, one "trick":
    ```
    struct custom_tag{};
    void read_bytes(wire::reader&, boost::fusion::pair<custom_tag, std::string&>)
    { ... }
    void write_bytes(wire::writer&, boost::fusion::pair<custom_tag, const std::string&>)
    { ... }

    template<typename F, typename T>
    void object_map(F& format, T& self)
    {
      wire::object(format,
        wire::field("foo", boost::fusion::make_pair<custom_tag>(std::ref(self.foo)))
      );
    }
    ```

    Basically each input/output format needs a unique type so that the compiler
    knows how to "dispatch" the read/write calls. */
  template<typename T, bool Required>
  struct field_
  {
    using value_type = unwrap_reference_t<T>;

    //! \return True if field is forced optional when `get_value().empty()`.
    static constexpr bool optional_on_empty() noexcept
    { return is_optional_on_empty<value_type>::value; }

    static constexpr bool is_required() noexcept { return Required && !optional_on_empty(); }
    static constexpr std::size_t count() noexcept { return 1; }

    const char* name;
    T value;

    constexpr const value_type& get_value() const noexcept { return value; }
    value_type& get_value() noexcept { return value; }
  };

  //! Links `name` to `value`. Use `std::ref` if de-serializing.
  template<typename T>
  constexpr inline field_<T, true> field(const char* name, T value)
  {
    return {name, std::move(value)};
  }

  //! Links `name` to optional `value`. Use `std::ref` if de-serializing.
  template<typename T>
  constexpr inline field_<T, false> optional_field(const char* name, T value)
  {
    return {name, std::move(value)};
  }


  template<typename T>
  inline constexpr bool available(const field_<T, true>& elem)
  {
    /* The old output engine always skipped fields when it was an empty array,
       this follows that behavior. See comments for `field_`. */
    return elem.is_required() || (elem.optional_on_empty() && !wire::empty(elem.get_value()));
  }
  template<typename T>
  inline constexpr bool available(const field_<T, false>& elem)
  {
    return bool(elem.get_value());
  }
} // wire