boost_variant.hpp

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#pragma once
 
/// @file userver/formats/parse/boost_variant.hpp
/// @brief Ineffective but generic parser for boost::variant type
///
/// Parsing is performed for each of the N alternatives in variant, N-1
/// exceptions is thrown and caught during the parsing.
///
/// @ingroup userver_universal userver_formats_parse
 
#include <boost/variant/variant.hpp>
 
#include <userver/compiler/demangle.hpp>
#include <userver/formats/parse/variant.hpp>
 
USERVER_NAMESPACE_BEGIN
 
namespace formats::parse {
 
namespace impl {
template <class T, class Value, typename Result>
void ParseBoostVariantSingle(const Value& value,
                             std::optional<Result>& result) {
  if (result) {
    std::type_index old_type = result->type();
    try {
      value.template As<T>();
    } catch (const std::exception&) {
      return;
    }
 
    ThrowVariantAmbiguousParse<typename Value::ParseException, Result, T>(
        value.GetPath(), old_type);
  } else {
    // No result yet
    try {
      result = value.template As<T>();
    } catch (const std::exception&) {
    }
  }
}
 
}  // namespace impl
 
template <class Value, typename... Types>
boost::variant<Types...> Parse(const Value& value,
                               formats::parse::To<boost::variant<Types...>>) {
  std::optional<boost::variant<Types...>> result;
  (impl::ParseBoostVariantSingle<Types>(value, result), ...);
 
  if (!result) {
    ThrowVariantParseException<typename Value::ParseException,
                               boost::variant<Types...>>(value.GetPath());
  }
 
  return std::move(*result);
}
 
}  // namespace formats::parse
 
USERVER_NAMESPACE_END