Iterators for Ranges of Dates with day steps

components/calendar/Cargo.toml

@@ -77,3 +77,6 @@ name = "iso_date_manipulations"
 
 [[example]]
 name = "iso_datetime_manipulations"
+
+[[example]]
+name = "iso_date_range_iter"

components/calendar/examples/iso_date_range_iter.rs

@@ -0,0 +1,46 @@
+// This file is part of ICU4X. For terms of use, please see the file
+// called LICENSE at the top level of the ICU4X source tree
+// (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).
+
+// An example application which uses date range iteration.
+
+#![no_main] // https://github.com/unicode-org/icu4x/issues/395
+icu_benchmark_macros::instrument!();
+use icu_benchmark_macros::println;
+
+use icu_calendar::range::ToDateIter;
+use icu_calendar::{Date, Iso};
+
+fn print_date(date: Date<Iso>) {
+    let year = date.year().era_year_or_extended();
+    let mon = date.month().ordinal;
+    let day = date.day_of_month().0;
+    println!("Date: {day:02} {mon:02} {year}");
+}
+
+fn print_space() {
+    println!("");
+}
+
+fn main() {
+    let date_from = Date::try_new_iso(2024, 11, 29).unwrap();
+    let date_to = Date::try_new_iso(2025, 3, 31).unwrap();
+
+    // Let's print 10 dates from infinity date range:
+    let inf_range = date_from..;
+    inf_range.to_date_iter().take(10).for_each(print_date);
+
+    print_space();
+
+    // Let's print each 13th date from non-infinity range:
+    let range = date_from..date_to;
+    let iter = range.to_date_iter().step_by(13);
+    iter.for_each(print_date);
+
+    print_space();
+
+    // Let's print each 13th date from reversed non-infinity range:
+    let range_inclusive = date_from..=date_to;
+    let iter = range_inclusive.to_date_iter().rev().step_by(13);
+    iter.for_each(print_date);
+}

components/calendar/src/chinese.rs

@@ -106,7 +106,7 @@ pub struct Chinese {
 
 /// The inner date type used for representing [`Date`]s of [`Chinese`]. See [`Date`] and [`Chinese`] for more details.
 #[derive(Debug, Eq, PartialEq, PartialOrd, Ord)]
-pub struct ChineseDateInner(ChineseBasedDateInner<Chinese>);
+pub struct ChineseDateInner(pub(crate) ChineseBasedDateInner<Chinese>);
 
 type Inner = ChineseBasedDateInner<Chinese>;
 

components/calendar/src/iso.rs

@@ -334,17 +334,21 @@ impl Iso {
         Date::try_new_iso(year, month, day).unwrap()
     }
     pub(crate) fn iso_from_fixed(date: RataDie) -> Date<Iso> {
-        let (year, month, day) = match calendrical_calculations::iso::iso_from_fixed(date) {
+        match Self::iso_try_from_fixed(date) {
+            Ok(date) => date,
             Err(I32CastError::BelowMin) => {
-                return Date::from_raw(IsoDateInner(ArithmeticDate::min_date()), Iso)
+                Date::from_raw(IsoDateInner(ArithmeticDate::min_date()), Iso)
             }
             Err(I32CastError::AboveMax) => {
-                return Date::from_raw(IsoDateInner(ArithmeticDate::max_date()), Iso)
+                Date::from_raw(IsoDateInner(ArithmeticDate::max_date()), Iso)
             }
-            Ok(ymd) => ymd,
-        };
-        #[allow(clippy::unwrap_used)] // valid day and month
-        Date::try_new_iso(year, month, day).unwrap()
+        }
+    }
+    pub(crate) fn iso_try_from_fixed(date: RataDie) -> Result<Date<Iso>, I32CastError> {
+        calendrical_calculations::iso::iso_from_fixed(date).map(|(year, month, day)| {
+            #[allow(clippy::unwrap_used)] // valid day and month
+            Date::try_new_iso(year, month, day).unwrap()
+        })
     }
 
     pub(crate) fn day_of_year(date: IsoDateInner) -> u16 {

components/calendar/src/lib.rs

@@ -212,3 +212,6 @@ pub use gregorian::Gregorian;
 #[doc(no_inline)]
 pub use iso::Iso;
 pub use types::Time;
+
+/// Ranges for `Date` struct
+pub mod range;