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Merged
ktf merged 2 commits into from
Dec 2, 2020
Merged

DPL: add compile-time string concat and support std::string_view #4975

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12db3cb
DPL: add compile-time string concat and support std::string_view
mario-krueger Dec 2, 2020
7b5498a
make operator constexpr
mario-krueger Dec 2, 2020
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57 changes: 47 additions & 10 deletions Framework/Core/include/Framework/StringHelpers.h
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Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,7 @@
#include <cstdint>
#include <utility>
#include <type_traits>
#include <string_view>

// CRC32 Table (zlib polynomial) static
constexpr uint32_t crc_table[256] = {0x0L, 0x77073096L, 0xee0e612cL,
Expand Down Expand Up @@ -102,6 +103,15 @@ constexpr bool is_const_str_v(T)
return is_const_str<T>::value;
}

template <char... chars1, char... chars2>
constexpr auto operator+(const ConstStr<chars1...>&, const ConstStr<chars2...>&)
{
return ConstStr<chars1..., chars2...>{};
}

namespace const_str_details
{

template <typename T, std::size_t... Is>
constexpr auto as_chars_impl(std::index_sequence<Is...>)
{
Expand All @@ -112,18 +122,45 @@ template <typename T>
constexpr auto as_chars()
{
return as_chars_impl<T>(
std::make_index_sequence<sizeof(T::str()) - 1>{});
std::make_index_sequence<T::size() - 1>{});
}

template <int N>
constexpr const char* const get_str(const char (&str)[N])
{
return str;
}

template <int N>
constexpr const int get_size(const char (&str)[N])
{
return N;
}

constexpr const char* const get_str(const std::string_view& str)
{
return str.data();
}

constexpr const int get_size(const std::string_view& str)
{
return str.size() + 1;
}
} // namespace const_str_details

#define CONST_STR(literal) \
[] { \
struct literal_to_chars { \
static constexpr decltype(auto) str() \
{ \
return literal; \
} \
}; \
return as_chars<literal_to_chars>(); \
#define CONST_STR(literal) \
[] { \
struct literal_to_chars { \
static constexpr decltype(auto) str() \
{ \
return const_str_details::get_str(literal); \
} \
static constexpr decltype(auto) size() \
{ \
return const_str_details::get_size(literal); \
} \
}; \
return const_str_details::as_chars<literal_to_chars>(); \
}()

#endif // O2_FRAMEWORK_STRINGHELPERS_H
18 changes: 18 additions & 0 deletions Framework/Core/test/test_StringHelpers.cxx
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Original file line number Diff line number Diff line change
Expand Up @@ -48,4 +48,22 @@ BOOST_AUTO_TEST_CASE(StringHelpersConstStr)
if constexpr (is_const_str_v(myConstStr)) {
std::cout << "myConstStr is a compile-time string" << std::endl;
}

auto myConstStr2 = CONST_STR("hello") + CONST_STR("Universe");
printString(myConstStr2);
static_assert(std::is_same_v<decltype(myConstStr2), ConstStr<'h', 'e', 'l', 'l', 'o', 'U', 'n', 'i', 'v', 'e', 'r', 's', 'e'>>);

enum ParticleSpecies {
kPion,
kKaon
};
static constexpr std::string_view hist[] = {"ptDist", "etaDist"};
static constexpr std::string_view particleSuffix[] = {"_pions", "_kaons"};

printString(CONST_STR(hist[0]) + CONST_STR(particleSuffix[kPion]));
printString(CONST_STR(hist[0]) + CONST_STR(particleSuffix[kKaon]));
printString(CONST_STR(hist[1]) + CONST_STR(particleSuffix[kPion]));
printString(CONST_STR(hist[1]) + CONST_STR(particleSuffix[kKaon]));

BOOST_CHECK_EQUAL(CONST_STR(hist[0]).hash, CONST_STR("ptDist").hash);
}