algo.hpp

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#pragma once
 
/// @file userver/utils/algo.hpp
/// @brief Small useful algorithms.
/// @ingroup userver_universal
 
#include <algorithm>
#include <cstddef>
#include <iterator>
#include <optional>
#include <string>
#include <string_view>
#include <type_traits>
#include <utility>
 
#include <userver/utils/checked_pointer.hpp>
 
USERVER_NAMESPACE_BEGIN
 
namespace utils {
 
/// @brief Concatenates multiple `std::string_view`-convertible items
template <typename ResultString = std::string, typename... Strings>
ResultString StrCat(const Strings&... strings) {
    return [](auto... string_views) {
        std::size_t result_size = 0;
        ((result_size += string_views.size()), ...);
 
        ResultString result;
        result.reserve(result_size);
        (result.append(string_views), ...);
        return result;
    }(std::string_view{strings}...);
}
 
/// @brief Returns nullptr if no key in associative container, otherwise
/// returns pointer to value.
template <class Map, class Key>
auto* FindOrNullptr(Map& map, const Key& key) {
    const auto it = map.find(key);
    return (it == map.end() ? nullptr : &it->second);
}
 
/// @brief Returns default value if no key in associative container, otherwise
/// returns a copy of the stored value.
template <class Map, class Key, class Default>
typename Map::mapped_type FindOrDefault(Map& map, const Key& key, Default&& def) {
    const auto* ptr = utils::FindOrNullptr(map, key);
    if (!ptr) {
        return {std::forward<Default>(def)};
    }
    return *ptr;
}
 
/// @brief Returns default value if no key in associative container, otherwise
/// returns a copy of the stored value.
template <class Map, class Key>
typename Map::mapped_type FindOrDefault(Map& map, const Key& key) {
    const auto ptr = USERVER_NAMESPACE::utils::FindOrNullptr(map, key);
    if (!ptr) {
        return {};
    }
    return *ptr;
}
 
/// @brief Returns std::nullopt if no key in associative container, otherwise
/// returns std::optional with a copy of value
template <class Map, class Key>
std::optional<typename Map::mapped_type> FindOptional(Map& map, const Key& key) {
    const auto ptr = utils::FindOrNullptr(map, key);
    if (!ptr) {
        return std::nullopt;
    }
    return {*ptr};
}
 
/// @brief Searches a map for an element and return a checked pointer to
/// the found element
template <typename Map, typename Key>
auto CheckedFind(Map& map, const Key& key) -> decltype(utils::MakeCheckedPtr(&map.find(key)->second)) {
    if (auto f = map.find(key); f != map.end()) {
        return utils::MakeCheckedPtr(&f->second);
    }
    return {nullptr};
}
 
/// @brief Converts one container type to another
template <class ToContainer, class FromContainer>
ToContainer AsContainer(FromContainer&& container) {
    if constexpr (std::is_rvalue_reference_v<decltype(container)>) {
        return ToContainer(
            std::make_move_iterator(std::begin(container)), std::make_move_iterator(std::end(container))
        );
    } else {
        return ToContainer(std::begin(container), std::end(container));
    }
}
 
namespace impl {
template <typename Container, typename = void>
struct HasKeyType : std::false_type {};
 
template <typename Container>
struct HasKeyType<Container, std::void_t<typename Container::key_type>> : std::true_type {};
 
template <typename Container>
inline constexpr bool kHasKeyType = HasKeyType<Container>::value;
}  // namespace impl
 
/// @brief Erased elements and returns number of deleted elements
template <class Container, class Pred>
auto EraseIf(Container& container, Pred pred) {
    if constexpr (impl::kHasKeyType<Container>) {
        auto old_size = container.size();
        for (auto it = std::begin(container), last = std::end(container); it != last;) {
            if (pred(*it)) {
                it = container.erase(it);
            } else {
                ++it;
            }
        }
        return old_size - container.size();
    } else {
        auto it = std::remove_if(std::begin(container), std::end(container), pred);
        const auto removed = std::distance(it, std::end(container));
        container.erase(it, std::end(container));
        return removed;
    }
}
 
/// @brief Erased elements and returns number of deleted elements
template <class Container, class T>
size_t Erase(Container& container, const T& elem) {
    if constexpr (impl::kHasKeyType<Container>) {
        return container.erase(elem);
    } else {
        // NOLINTNEXTLINE(readability-qualified-auto)
        auto it = std::remove(std::begin(container), std::end(container), elem);
        const auto removed = std::distance(it, std::end(container));
        container.erase(it, std::end(container));
        return removed;
    }
}
 
/// @brief returns true if there is an element in container which satisfies
/// the predicate
template <typename Container, typename Pred>
bool ContainsIf(const Container& container, Pred pred) {
    return std::find_if(std::begin(container), std::end(container), pred) != std::end(container);
}
 
}  // namespace utils
 
USERVER_NAMESPACE_END