std::chrono..._conversion(3)

🎀 std::chrono::clock_time_conversion 🎀

okay so bestie, welcome to the std::chrono..._conversion(3) page from the C++ Standard Libary 💖 this one is all about std::chrono::clock_time_conversion, and it's lowkey the backstage matchmaker that tells your time points how to clock-shift. let's get into the vibe ✨

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🌸 NAME 🌸

std::chrono::clock_time_conversion — literally std::chrono::clock_time_conversion, the trait bestie. iconic name, no notes 💅

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✨ Synopsis ✨

Defined in header <chrono>.

template< class Dest, class Source >
struct clock_time_conversion {};

(since C++20)

std::chrono::clock_time_conversion is a trait that specifies how to convert a std::chrono::time_point of the Source clock to that of the Dest clock. It does that by providing a const-callable operator() that accepts an argument of type std::chrono::time_point<Source, Duration> and returns a std::chrono::time_point<Dest, OtherDuration> that represents an equivalent point in time. The duration of the returned time point is computed from the source duration in a manner that varies for each specialization. iykyk 🫶

clock_time_conversion is normally only used indirectly, via std::chrono::clock_cast — so most of the time it's just doing its little backstage thing while you live your life 🎬

A program may specialize clock_time_conversion if at least one of the template parameters is a user-defined clock type.

The primary template is an empty struct. The standard defines the following specializations:

• (1) (since C++20)

template< class Clock >
struct clock_time_conversion<Clock, Clock>;

• (2) (since C++20)

template<>
struct clock_time_conversion<std::chrono::system_clock, std::chrono::system_clock>;

• (3) (since C++20)

template<>
struct clock_time_conversion<std::chrono::utc_clock, std::chrono::utc_clock>;

• (4) (since C++20)

template<>
struct clock_time_conversion<std::chrono::system_clock, std::chrono::utc_clock>;

• (5) (since C++20)

template<>
struct clock_time_conversion<std::chrono::utc_clock, std::chrono::system_clock>;

• (6) (since C++20)

template< class Clock >
struct clock_time_conversion<Clock, std::chrono::system_clock>;

• (7) (since C++20)

template< class Clock >
struct clock_time_conversion<std::chrono::system_clock, Clock>;

• (8) (since C++20)

template< class Clock >
struct clock_time_conversion<Clock, std::chrono::utc_clock>;

• (9) (since C++20)

template< class Clock >
struct clock_time_conversion<std::chrono::utc_clock, Clock>;

okay so the behavior breakdown, bestie:

• 1-3) Identity conversion: operator() returns a copy of the argument.
• 4,5) Conversions between std::chrono::sys_time and std::chrono::utc_time: operator() calls std::chrono::utc_clock::to_sys and std::chrono::utc_clock::from_sys, respectively.
• 6,7) Conversions to and from std::chrono::sys_time when Clock supports from_sys and to_sys: operator() calls Clock::to_sys and Clock::from_sys, respectively.
• 8,9) Conversions to and from std::chrono::utc_time when Clock supports from_utc and to_utc: operator() calls Clock::to_utc and Clock::from_utc, respectively.

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🛠️ Member functions 🛠️

Each specialization has an implicitly-declared default constructor, copy constructor, move constructor, copy assignment operator, move assignment operator, and destructor. yes, all of them, slay 💅

🌟 std::chrono::clock_time_conversion::operator() 🌟

• (1) — member of specialization (1):

template< class Duration >
std::chrono::time_point<Clock, Duration>
operator()( const std::chrono::time_point<Clock, Duration>& t ) const;

• (2) — member of specialization (2):

template< class Duration >
std::chrono::sys_time<Duration>
operator()( const std::chrono::sys_time<Duration> & t ) const;

• (3) — member of specialization (3):

template< class Duration >
std::chrono::utc_time<Duration>
operator()( const std::chrono::utc_time<Duration>& t ) const;

• (4) — member of specialization (4):

template< class Duration >
std::chrono::sys_time<Duration>
operator()( const std::chrono::utc_time<Duration>& t ) const;

• (5) — member of specialization (5):

template< class Duration >
std::chrono::utc_time<Duration>
operator()( const std::chrono::sys_time<Duration>& t ) const;

• (6) — member of specialization (6):

template< class Duration >
auto operator()( const std::chrono::sys_time<Duration>& t ) const
    -> decltype(Clock::from_sys(t));

• (7) — member of specialization (7):

template< class Duration >
auto operator()( const std::chrono::time_point<SourceClock, Duration>& t ) const
    -> decltype(Clock::to_sys(t));

• (8) — member of specialization (8):

template< class Duration >
auto operator()( const std::chrono::utc_time<Duration>& t ) const
    -> decltype(Clock::from_utc(t));

• (9) — member of specialization (9):

template< class Duration >
auto operator()( const std::chrono::time_point<Clock, Duration>& t ) const
    -> decltype(Clock::to_utc(t));

Converts the argument std::chrono::time_point to the destination clock. 🕰️✨

• 1-3) Identity conversion. Returns t unchanged.
• 4) Returns std::chrono::utc_clock::to_sys(t).
• 5) Returns std::chrono::utc_clock::from_sys(t).
• 6) Returns Clock::from_sys(t). This overload participates in overload resolution only if the expression Clock::from_sys(t) is well-formed. The program is ill-formed if Clock::from_sys(t) does not return std::chrono::time_point<Clock, Duration> where Duration is some valid specialization of std::chrono::duration.
• 7) Returns Clock::to_sys(t). This overload participates in overload resolution only if the expression Clock::to_sys(t) is well-formed. The program is ill-formed if Clock::to_sys(t) does not return std::chrono::sys_time<Duration> where Duration is some valid specialization of std::chrono::duration.
• 8) Returns Clock::from_utc(t). This overload participates in overload resolution only if the expression Clock::from_utc(t) is well-formed. The program is ill-formed if Clock::from_utc(t) does not return std::chrono::time_point<Clock, Duration> where Duration is some valid specialization of std::chrono::duration.
• 9) Returns Clock::to_utc(t). This overload participates in overload resolution only if the expression Clock::to_utc(t) is well-formed. The program is ill-formed if Clock::to_utc(t) does not return std::chrono::utc_time<Duration> where Duration is some valid specialization of std::chrono::duration.

bestie, if you see ill-formed in there, that's not a cute vibe — it means the program is not valid. take it seriously 💀

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🫶 Parameters 🫶

• t — time point to convert

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🌈 Return value 🌈

The result of the conversion as described above:

• 1-3) t.
• 4) std::chrono::utc_clock::to_sys(t).
• 5) std::chrono::utc_clock::from_sys(t).
• 6) Clock::from_sys(t).
• 7) Clock::to_sys(t).
• 8) Clock::from_utc(t).
• 9) Clock::to_utc(t).

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👀 See also 👀

• clock_cast — convert time points of one clock to another; (C++20) (function template)

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mwah 💋 this cutie came from source http://cppreference.com, with version/date 2024.06.10, and the page stamp is std::chrono..._conversion(3). that's the whole vibe, bye bestie! 🫶✨