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Add valueOrNullptr and valueOrDefault utilities.

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This commit is contained in:
Daniel Kirchner 2021-01-11 19:59:06 +01:00
parent 67d21a87c5
commit f5adaa8bbb
1 changed files with 33 additions and 0 deletions
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33
libsolutil/CommonData.h
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@ -232,6 +232,39 @@ std::set<K> keys(std::map<K, V> const& _map)
return applyMap(_map, [](auto const& _elem) { return _elem.first; }, std::set<K>{});
}
/// @returns a pointer to the entry of @a _map at @a _key, if there is one, and nullptr otherwise.
template<typename MapType, typename KeyType>
decltype(auto) valueOrNullptr(MapType&& _map, KeyType const& _key)
{
auto it = _map.find(_key);
return (it == _map.end()) ? nullptr : &it->second;
}
namespace detail
{
struct allow_copy {};
}
static constexpr auto allow_copy = detail::allow_copy{};
/// @returns a reference to the entry of @a _map at @a _key, if there is one, and @a _defaultValue otherwise.
/// Makes sure no copy is involved, unless allow_copy is passed as fourth argument.
template<
typename MapType,
typename KeyType,
typename ValueType = std::decay_t<decltype(std::declval<MapType>().find(std::declval<KeyType>())->second)> const&,
typename AllowCopyType = void*
>
decltype(auto) valueOrDefault(MapType&& _map, KeyType const& _key, ValueType&& _defaultValue = {}, AllowCopyType = nullptr)
{
auto it = _map.find(_key);
static_assert(
std::is_same_v<AllowCopyType, detail::allow_copy> ||
std::is_reference_v<decltype((it == _map.end()) ? _defaultValue : it->second)>,
"valueOrDefault does not allow copies by default. Pass allow_copy as additional argument, if you want to allow copies."
);
return (it == _map.end()) ? _defaultValue : it->second;
}
// String conversion functions, mainly to/from hex/nibble/byte representations.
enum class WhenError