#include <userver/utils/trivial_map.hpp>

Detailed Description

template<typename BuilderFunc>
class utils::TrivialBiMap< BuilderFunc >

Bidirectional unordered map for trivial types, including string literals; could be efficiently used as a unordered non-bidirectional map.

constexpr utils::TrivialBiMap kToInt = [](auto selector) {
    return selector().Case("zero", 0).Case("one", 1).Case("two", 2).Case("three", 3).Case("four", 4);
};
 
TEST(TrivialBiMap, StringBasic) {
    EXPECT_FALSE(kToInt.TryFind(42));
 
    EXPECT_EQ(kToInt.TryFind("one"), 1);
    EXPECT_EQ(kToInt.TryFind(2), "two");
 
    EXPECT_EQ(kToInt.TryFind("ten").value_or(-1), -1);
}

utils::TrivialBiMap and utils::TrivialSet are known to outperform std::unordered_map if:

there's 32 or less elements in map/set
or keys are string literals and all of them differ in length.

Implementation of string search is very efficient due to modern compilers optimize it to a switch by input string length and an integral comparison (rather than a std::memcmp call). In other words, it usually takes O(1) to find the match in the map.

The same story with integral or enum mappings - compiler optimizes them into a switch and it usually takes O(1) to find the match.

enum class Colors { kRed, kOrange, kYellow, kGreen, kBlue, kViolet };
enum ThirdPartyColor { kGreen, kBlue, kViolet, kRed, kOrange, kYellow };
 
constexpr utils::TrivialBiMap kColorSwitch = [](auto selector) {
    return selector()
        .Case(ThirdPartyColor::kRed, Colors::kRed)
        .Case(ThirdPartyColor::kOrange, Colors::kOrange)
        .Case(ThirdPartyColor::kYellow, Colors::kYellow)
        .Case(ThirdPartyColor::kGreen, Colors::kGreen)
        .Case(ThirdPartyColor::kBlue, Colors::kBlue)
        .Case(ThirdPartyColor::kViolet, Colors::kViolet);
};
 
TEST(TrivialBiMap, EnumToEnum) {
    EXPECT_EQ(kColorSwitch.TryFind(ThirdPartyColor::kRed), Colors::kRed);
    EXPECT_EQ(kColorSwitch.TryFind(ThirdPartyColor::kBlue), Colors::kBlue);
 
    EXPECT_EQ(kColorSwitch.TryFind(Colors::kGreen), ThirdPartyColor::kGreen);
    EXPECT_EQ(kColorSwitch.TryFind(Colors::kOrange), ThirdPartyColor::kOrange);
}

Empty map:

For a single value Case statements see utils::TrivialSet.

Definition at line 594 of file trivial_map.hpp.

Classes
class	iterator

struct	value_type

Public Types
using	First = typename TypesPair::first_type

using	Second = typename TypesPair::second_type

template<class T >
using	MappedTypeFor = std::conditional_t<std::is_convertible_v<T, First>, Second, First>

Public Member Functions
constexpr	TrivialBiMap (BuilderFunc &&func) noexcept

constexpr std::optional< Second >	TryFindByFirst (First value) const noexcept

constexpr std::optional< First >	TryFindBySecond (Second value) const noexcept

template<class T >
constexpr std::optional< MappedTypeFor< T > >	TryFind (T value) const noexcept

constexpr std::optional< Second >	TryFindICaseByFirst (std::string_view value) const noexcept
	Case insensitive search for value.

constexpr std::optional< First >	TryFindICaseBySecond (std::string_view value) const noexcept
	Case insensitive search for value.

constexpr std::optional< MappedTypeFor< std::string_view > >	TryFindICase (std::string_view value) const noexcept
	Case insensitive search for value that calls either TryFindICaseBySecond or TryFindICaseByFirst.

constexpr std::size_t	size () const noexcept
	Returns count of Case's in mapping.

std::string	Describe () const

std::string	DescribeFirst () const

std::string	DescribeSecond () const

template<typename T >
std::string	DescribeByType () const

constexpr value_type	GetValuesByIndex (std::size_t index) const

constexpr iterator	begin () const

constexpr iterator	end () const

constexpr iterator	cbegin () const

constexpr iterator	cend () const

Detailed Description

Classes

Public Types

Public Member Functions

Member Typedef Documentation

◆ First

◆ MappedTypeFor

◆ Second

Constructor & Destructor Documentation

◆ TrivialBiMap()

Member Function Documentation

◆ begin()

◆ cbegin()

◆ cend()

◆ Describe()

◆ DescribeByType()

◆ DescribeFirst()

◆ DescribeSecond()

◆ end()

◆ GetValuesByIndex()

◆ size()

◆ TryFind()

◆ TryFindByFirst()

◆ TryFindBySecond()

◆ TryFindICase()

◆ TryFindICaseByFirst()

◆ TryFindICaseBySecond()