return to the faster-performing version

crates/polars-core/src/fmt.rs

@@ -1019,13 +1019,12 @@ pub fn fmt_duration_string(mut v: i64, unit: TimeUnit, iso: bool) -> String {
         if v < 0 {
             // negative sign before "P" indicates that the entire ISO duration is negative.
             // the Polars version applies a negative sign to each *individual* part.
-            write!(s, "-P").unwrap();
+            s.push_str("-P");
             v = v.abs()
         } else {
-            write!(s, "P").unwrap();
+            s.push('P');
         }
     };
-
     // iterate over dtype-specific sizes to appropriately scale
     // and extract 'days', 'hours', 'minutes', and 'seconds' parts.
     for (i, &size) in sizes.iter().enumerate() {
@@ -1035,63 +1034,70 @@ pub fn fmt_duration_string(mut v: i64, unit: TimeUnit, iso: bool) -> String {
             (v % sizes[i - 1]) / size
         };
         if whole_num != 0 || (iso && i == 3) {
-            write!(s, "{}", buffer.format(whole_num)).unwrap();
+            s.push_str(buffer.format(whole_num));
             if iso {
                 // (index 3 => 'seconds' part): the ISO version writes
-                // fractional seconds, not nano/micro/milliseconds
+                // fractional seconds, not integer nano/micro/milliseconds.
                 if i == 3 {
                     let secs = match unit {
                         TimeUnit::Nanoseconds => format!(".{:09}", v % size),
                         TimeUnit::Microseconds => format!(".{:06}", v % size),
                         TimeUnit::Milliseconds => format!(".{:03}", v % size),
                     };
-                    write!(s, "{}", secs.trim_end_matches('0')).unwrap();
+                    s.push_str(secs.trim_end_matches('0'));
                 }
-                write!(s, "{}", ISO_DURATION_PARTS[i]).unwrap();
+                s.push_str(ISO_DURATION_PARTS[i]);
 
                 // (index 0 => 'days' part): after writing days above (if non-zero)
-                // the ISO duration string requires a `T` before the time part
+                // the ISO duration string requires a `T` before the time part.
                 if i == 0 {
-                    write!(s, "T").unwrap();
+                    s.push('T');
                 }
             } else {
-                write!(s, "{}", DURATION_PARTS[i]).unwrap();
+                s.push_str(DURATION_PARTS[i]);
                 if v % size != 0 {
-                    write!(s, " ").unwrap();
+                    s.push(' ');
                 }
             }
         } else if iso && i == 0 {
-            write!(s, "T").unwrap();
+            // always need to write the `T` separator for ISO
+            // durations, even if there is no 'days' part.
+            s.push('T');
         }
     }
     if iso {
-        // ISO version has already written fractional seconds (if non-zero)
+        // ISO version has already written out the fractional seconds (if non-zero).
         if s.ends_with('T') {
             s.pop();
         }
     } else {
-        // Polars version writes out fractional seconds separately as
-        // integer nano/micro/millseconds
+        // Polars version writes out fractional seconds as integer nano/micro/milliseconds.
         match unit {
             TimeUnit::Nanoseconds => {
                 if v % 1000 != 0 {
-                    write!(s, "{}ns", buffer.format(v % 1_000_000_000)).unwrap();
+                    s.push_str(buffer.format(v % 1_000_000_000));
+                    s.push_str("ns");
                 } else if v % 1_000_000 != 0 {
-                    write!(s, "{}µs", buffer.format((v % 1_000_000_000) / 1000)).unwrap();
+                    s.push_str(buffer.format((v % 1_000_000_000) / 1000));
+                    s.push_str("µs");
                 } else if v % 1_000_000_000 != 0 {
-                    write!(s, "{}ms", buffer.format((v % 1_000_000_000) / 1_000_000)).unwrap();
+                    s.push_str(buffer.format((v % 1_000_000_000) / 1_000_000));
+                    s.push_str("ms");
                 }
             },
             TimeUnit::Microseconds => {
                 if v % 1000 != 0 {
-                    write!(s, "{}µs", buffer.format(v % 1_000_000)).unwrap();
+                    s.push_str(buffer.format(v % 1_000_000));
+                    s.push_str("µs");
                 } else if v % 1_000_000 != 0 {
-                    write!(s, "{}ms", buffer.format((v % 1_000_000) / 1_000)).unwrap();
+                    s.push_str(buffer.format((v % 1_000_000) / 1_000));
+                    s.push_str("ms");
                 }
             },
             TimeUnit::Milliseconds => {
                 if v % 1000 != 0 {
-                    write!(s, "{}ms", buffer.format(v % 1_000)).unwrap();
+                    s.push_str(buffer.format(v % 1_000));
+                    s.push_str("ms");
                 }
             },
         }