doki23 commented on code in PR #3762:
URL: https://github.com/apache/arrow-rs/pull/3762#discussion_r1126659594


##########
arrow-cast/src/parse.rs:
##########
@@ -445,6 +446,231 @@ impl Parser for Date64Type {
     }
 }
 
+pub(crate) fn parse_interval_year_month(
+    value: &str,
+) -> Result<<IntervalYearMonthType as ArrowPrimitiveType>::Native, ArrowError> 
{
+    let (result_months, result_days, result_nanos) = parse_interval("years", 
value)?;
+    if result_days != 0 || result_nanos != 0 {
+        return Err(ArrowError::CastError(format!(
+            "Cannot cast {value} to IntervalYearMonth because the value isn't 
multiple of months"
+        )));
+    }
+    Ok(IntervalYearMonthType::make_value(0, result_months))
+}
+
+pub(crate) fn parse_interval_day_time(
+    value: &str,
+) -> Result<<IntervalDayTimeType as ArrowPrimitiveType>::Native, ArrowError> {
+    let (result_months, mut result_days, result_nanos) = 
parse_interval("days", value)?;
+    if result_nanos % 1_000_000 != 0 {
+        return Err(ArrowError::CastError(format!(
+            "Cannot cast {value} to IntervalDayTime because the nanos part 
isn't multiple of milliseconds"
+        )));
+    }
+    result_days += result_months * 30;
+    Ok(IntervalDayTimeType::make_value(
+        result_days,
+        (result_nanos / 1_000_000) as i32,
+    ))
+}
+
+pub(crate) fn parse_interval_month_day_nano(
+    value: &str,
+) -> Result<<IntervalMonthDayNanoType as ArrowPrimitiveType>::Native, 
ArrowError> {
+    let (result_months, result_days, result_nanos) = parse_interval("months", 
value)?;
+    Ok(IntervalMonthDayNanoType::make_value(
+        result_months,
+        result_days,
+        result_nanos,
+    ))
+}
+
+const SECONDS_PER_HOUR: f64 = 3_600_f64;
+const NANOS_PER_MILLIS: f64 = 1_000_000_f64;
+const NANOS_PER_SECOND: f64 = 1_000_f64 * NANOS_PER_MILLIS;
+const NANOS_PER_MINUTE: f64 = 60_f64 * NANOS_PER_SECOND;
+const NANOS_PER_HOUR: f64 = 60_f64 * NANOS_PER_MINUTE;
+const NANOS_PER_DAY: f64 = 24_f64 * NANOS_PER_HOUR;
+
+#[derive(Clone, Copy)]
+#[repr(u16)]
+enum IntervalType {
+    Century = 0b_00_0000_0001,
+    Decade = 0b_00_0000_0010,
+    Year = 0b_00_0000_0100,
+    Month = 0b_00_0000_1000,
+    Week = 0b_00_0001_0000,
+    Day = 0b_00_0010_0000,
+    Hour = 0b_00_0100_0000,
+    Minute = 0b_00_1000_0000,
+    Second = 0b_01_0000_0000,
+    Millisecond = 0b_10_0000_0000,
+}
+
+impl FromStr for IntervalType {
+    type Err = ArrowError;
+
+    fn from_str(s: &str) -> Result<Self, ArrowError> {
+        match s.to_lowercase().as_str() {
+            "century" | "centuries" => Ok(Self::Century),
+            "decade" | "decades" => Ok(Self::Decade),
+            "year" | "years" => Ok(Self::Year),
+            "month" | "months" => Ok(Self::Month),
+            "week" | "weeks" => Ok(Self::Week),
+            "day" | "days" => Ok(Self::Day),
+            "hour" | "hours" => Ok(Self::Hour),
+            "minute" | "minutes" => Ok(Self::Minute),
+            "second" | "seconds" => Ok(Self::Second),
+            "millisecond" | "milliseconds" => Ok(Self::Millisecond),
+            _ => Err(ArrowError::NotYetImplemented(format!(
+                "Unknown interval type: {s}"
+            ))),
+        }
+    }
+}
+
+pub type MonthDayNano = (i32, i32, i64);
+
+/// parse string value to a triple of aligned months, days, nanos
+pub fn parse_interval(
+    leading_field: &str,
+    value: &str,
+) -> Result<MonthDayNano, ArrowError> {
+    let mut used_interval_types = 0;
+
+    let mut calculate_from_part = |interval_period_str: &str,
+                                   interval_type: &str|
+     -> Result<(i64, i64, f64), ArrowError> {

Review Comment:
   It's because smaller units can be converted to larger units. For instance, 
(i32::MAX + x) days can spill `(i32::MAX + x) / 30` months to the month part.



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