Motivation
Motivation
Working with dates, times, and time intervals is a fundamental requirement in almost all modern scientific computing disciplines (e.g., parsing climate datasets, writing logs, calculating intervals in financial models, astrophysical simulations).
Presently, Fortran provides the date_and_time() intrinsic subroutine, which returns an integer array values(1:8) containing components like year, month, day, hour, etc. However, performing any mathematical operations on these dates—such as adding 90 days to a timestamp or finding the total seconds between two events—forces the developer to write complex calendar logic from scratch to handle leap years, varying month lengths, and timezones.
I propose the addition of a comprehensive stdlib_datetime module to provide a high-level representation of Dates, Times, and Time Deltas (Intervals). This feature would bridge a significant gap with other modern languages like Python (datetime), C++ (std::chrono), and Java (java.time).
Proposed Interfaces and Derived Types
To provide robust time handling, the module would likely define three primary derived types:
datetime_type: Represents a specific point in time (Year, Month, Day, Hour, Minute, Second, Millisecond).timedelta_type: Represents a duration or an interval of time (Days, Seconds, Milliseconds).date_type / time_type: Smaller sub-types if separating only the calendar date from the clock time is deemed necessary.
Basic Usage Example:
use stdlib_datetime, only: datetime_type, timedelta_type, now, parse_date
type(datetime_type) :: t1, t2
type(timedelta_type) :: duration
! Get the current local time
t1 = now()
! Parse an ISO 8601 string easily
t2 = parse_date('2026-03-17T12:00:00Z')
! Calculate the difference between them
duration = t1 - t2
! Add an interval (e.g., 30 days) to a date
t2 = t2 + timedelta_type(days=30)Required Functionality:
- Constructors: from year/month/day components, from intrinsic
date_and_time arrays, and from ISO 8601 strings.
- Overloaded Operators (
+, -, ==, <, >): For adding timedelta_type to datetime_type, subtracting dates to get an interval, and comparing dates.
- Component Extraction: Helper functions to extract specific elements (e.g.,
t%year(), t%day_of_week(), t%is_leap_year()).
- Formatting: Easy output to strings (
'YYYY-MM-DD HH:MM:SS').
Prior Art
- Python: The
datetime module is universally used to structure Python time calculations.
- C++: The
<chrono> library provides durations, clocks, and time points.
- MATLAB: The
datetime and duration arrays.
- Fortran libraries: There are various custom implementations scattered across GitHub (e.g., M. Hirsch's
datetime-fortran), proving the extreme community demand for a standardized, native approach.
Additional Information
Implementing this module requires no complex C-bindings and no parameterized derived types (PDTs) (meaning compiler support will be near 100%). It is purely mathematical (Julian day calculations) and string manipulation, meaning it is easy to implement yet incredibly high impact for anyone doing data-wrangling in Fortran.
Motivation
Motivation
Working with dates, times, and time intervals is a fundamental requirement in almost all modern scientific computing disciplines (e.g., parsing climate datasets, writing logs, calculating intervals in financial models, astrophysical simulations).
Presently, Fortran provides the
date_and_time()intrinsic subroutine, which returns an integer arrayvalues(1:8)containing components like year, month, day, hour, etc. However, performing any mathematical operations on these dates—such as adding 90 days to a timestamp or finding the total seconds between two events—forces the developer to write complex calendar logic from scratch to handle leap years, varying month lengths, and timezones.I propose the addition of a comprehensive
stdlib_datetimemodule to provide a high-level representation of Dates, Times, and Time Deltas (Intervals). This feature would bridge a significant gap with other modern languages like Python (datetime), C++ (std::chrono), and Java (java.time).Proposed Interfaces and Derived Types
To provide robust time handling, the module would likely define three primary derived types:
datetime_type: Represents a specific point in time (Year, Month, Day, Hour, Minute, Second, Millisecond).timedelta_type: Represents a duration or an interval of time (Days, Seconds, Milliseconds).date_type/time_type: Smaller sub-types if separating only the calendar date from the clock time is deemed necessary.Basic Usage Example:
Required Functionality:
date_and_timearrays, and from ISO 8601 strings.+,-,==,<,>): For addingtimedelta_typetodatetime_type, subtracting dates to get an interval, and comparing dates.t%year(),t%day_of_week(),t%is_leap_year()).'YYYY-MM-DD HH:MM:SS').Prior Art
datetimemodule is universally used to structure Python time calculations.<chrono>library provides durations, clocks, and time points.datetimeanddurationarrays.datetime-fortran), proving the extreme community demand for a standardized, native approach.Additional Information
Implementing this module requires no complex C-bindings and no parameterized derived types (PDTs) (meaning compiler support will be near 100%). It is purely mathematical (Julian day calculations) and string manipulation, meaning it is easy to implement yet incredibly high impact for anyone doing data-wrangling in Fortran.