diff --git a/src/Clock/FixedClock.php b/src/Clock/FixedClock.php
index 29754cba..3a22e5d2 100644
--- a/src/Clock/FixedClock.php
+++ b/src/Clock/FixedClock.php
@@ -13,14 +13,11 @@
  */
 final class FixedClock implements Clock
 {
-    private Instant $instant;
-
     /**
      * @param Instant $instant The time to set the clock at.
      */
-    public function __construct(Instant $instant)
+    public function __construct(private Instant $instant)
     {
-        $this->instant = $instant;
     }
 
     public function getTime(): Instant
diff --git a/src/Clock/OffsetClock.php b/src/Clock/OffsetClock.php
index 14c1df12..d27cf282 100644
--- a/src/Clock/OffsetClock.php
+++ b/src/Clock/OffsetClock.php
@@ -13,24 +13,14 @@
  */
 final class OffsetClock implements Clock
 {
-    /**
-     * The reference clock.
-     */
-    private readonly Clock $referenceClock;
-
-    /**
-     * The offset to apply to the clock.
-     */
-    private readonly Duration $offset;
-
     /**
      * @param Clock    $referenceClock The reference clock.
      * @param Duration $offset         The offset to apply to the clock.
      */
-    public function __construct(Clock $referenceClock, Duration $offset)
-    {
-        $this->referenceClock = $referenceClock;
-        $this->offset = $offset;
+    public function __construct(
+        private readonly Clock $referenceClock,
+        private readonly Duration $offset
+    ) {
     }
 
     public function getTime(): Instant
diff --git a/src/Clock/ScaleClock.php b/src/Clock/ScaleClock.php
index e9da3817..3c478c25 100644
--- a/src/Clock/ScaleClock.php
+++ b/src/Clock/ScaleClock.php
@@ -13,21 +13,11 @@
  */
 final class ScaleClock implements Clock
 {
-    /**
-     * The reference clock.
-     */
-    private readonly Clock $referenceClock;
-
     /**
      * The start time.
      */
     private readonly Instant $startTime;
 
-    /**
-     * The time scale.
-     */
-    private readonly int $timeScale;
-
     /**
      * - a scale > 1 makes the time move at an accelerated pace;
      * - a scale == 1 makes the time move at the normal pace;
@@ -37,11 +27,11 @@ final class ScaleClock implements Clock
      * @param Clock $referenceClock The reference clock.
      * @param int   $timeScale      The time scale.
      */
-    public function __construct(Clock $referenceClock, int $timeScale)
-    {
-        $this->referenceClock = $referenceClock;
-        $this->startTime = $referenceClock->getTime();
-        $this->timeScale = $timeScale;
+    public function __construct(
+        private readonly Clock $referenceClock,
+        private readonly int $timeScale
+    ) {
+        $this->startTime = $this->referenceClock->getTime();
     }
 
     public function getTime(): Instant
diff --git a/src/Duration.php b/src/Duration.php
index 77d35834..472780b6 100644
--- a/src/Duration.php
+++ b/src/Duration.php
@@ -26,28 +26,17 @@
  */
 final class Duration implements JsonSerializable, Stringable
 {
-    /**
-     * The duration in seconds.
-     */
-    private readonly int $seconds;
-
-    /**
-     * The nanoseconds adjustment to the duration, in the range 0 to 999,999,999.
-     *
-     * A duration of -1 nanoseconds is stored as -1 seconds plus 999,999,999 nanoseconds.
-     */
-    private readonly int $nanos;
-
     /**
      * Private constructor. Use one of the factory methods to obtain a Duration.
      *
      * @param int $seconds The duration in seconds.
-     * @param int $nanos   The nanoseconds adjustment, validated in the range 0 to 999,999,999.
+     * @param int $nanos   The nanoseconds adjustment to the duration, validated in the range 0 to 999,999,999.
+     *                     A duration of -1 nanoseconds is stored as -1 seconds plus 999,999,999 nanoseconds.
      */
-    private function __construct(int $seconds, int $nanos = 0)
-    {
-        $this->seconds = $seconds;
-        $this->nanos = $nanos;
+    private function __construct(
+        private readonly int $seconds,
+        private readonly int $nanos = 0
+    ) {
     }
 
     /**
diff --git a/src/Instant.php b/src/Instant.php
index 14c17b3d..fca1a7d2 100644
--- a/src/Instant.php
+++ b/src/Instant.php
@@ -25,26 +25,16 @@
  */
 final class Instant implements JsonSerializable, Stringable
 {
-    /**
-     * The number of seconds since the epoch of 1970-01-01T00:00:00Z.
-     */
-    private readonly int $epochSecond;
-
-    /**
-     * The nanoseconds adjustment to the epoch second, in the range 0 to 999,999,999.
-     */
-    private readonly int $nano;
-
     /**
      * Private constructor. Use of() to obtain an Instant.
      *
-     * @param int $epochSecond The epoch second.
-     * @param int $nano        The nanosecond adjustment, validated in the range 0 to 999,999,999.
+     * @param int $epochSecond The number of seconds since the epoch of 1970-01-01T00:00:00Z.
+     * @param int $nano        The nanosecond adjustment to the epoch second, validated in the range 0 to 999,999,999.
      */
-    private function __construct(int $epochSecond, int $nano)
-    {
-        $this->epochSecond = $epochSecond;
-        $this->nano = $nano;
+    private function __construct(
+        private readonly int $epochSecond,
+        private readonly int $nano
+    ) {
     }
 
     /**
diff --git a/src/Interval.php b/src/Interval.php
index d8476964..0d477b18 100644
--- a/src/Interval.php
+++ b/src/Interval.php
@@ -16,23 +16,13 @@
 final class Interval implements JsonSerializable, Stringable
 {
     /**
-     * The start instant, inclusive.
+     * @param Instant $start The start instant, inclusive.
+     * @param Instant $end   The end instant, exclusive, validated as not before the start instant.
      */
-    private readonly Instant $start;
-
-    /**
-     * The end instant, exclusive.
-     */
-    private readonly Instant $end;
-
-    /**
-     * @param Instant $startInclusive The start instant, inclusive.
-     * @param Instant $endExclusive   The end instant, exclusive, validated as not before the start instant.
-     */
-    private function __construct(Instant $startInclusive, Instant $endExclusive)
-    {
-        $this->start = $startInclusive;
-        $this->end = $endExclusive;
+    private function __construct(
+        private readonly Instant $start,
+        private readonly Instant $end
+    ) {
     }
 
     /**
diff --git a/src/LocalDate.php b/src/LocalDate.php
index 59e4859d..1aecf047 100644
--- a/src/LocalDate.php
+++ b/src/LocalDate.php
@@ -48,21 +48,6 @@ final class LocalDate implements JsonSerializable, Stringable
      */
     public const DAYS_PER_CYCLE = 146097;
 
-    /**
-     * The year.
-     */
-    private readonly int $year;
-
-    /**
-     * The month-of-year.
-     */
-    private readonly int $month;
-
-    /**
-     * The day-of-month.
-     */
-    private readonly int $day;
-
     /**
      * Private constructor. Use of() to obtain an instance.
      *
@@ -70,11 +55,11 @@ final class LocalDate implements JsonSerializable, Stringable
      * @param int $month The month-of-year, validated from 1 to 12.
      * @param int $day   The day-of-month, validated from 1 to 31, valid for the year-month.
      */
-    private function __construct(int $year, int $month, int $day)
-    {
-        $this->year = $year;
-        $this->month = $month;
-        $this->day = $day;
+    private function __construct(
+        private readonly int $year,
+        private readonly int $month,
+        private readonly int $day
+    ) {
     }
 
     /**
diff --git a/src/LocalDateRange.php b/src/LocalDateRange.php
index 5c919b82..cb0673a2 100644
--- a/src/LocalDateRange.php
+++ b/src/LocalDateRange.php
@@ -26,24 +26,14 @@
  */
 final class LocalDateRange implements IteratorAggregate, Countable, JsonSerializable, Stringable
 {
-    /**
-     * The start date, inclusive.
-     */
-    private readonly LocalDate $start;
-
-    /**
-     * The end date, inclusive.
-     */
-    private readonly LocalDate $end;
-
     /**
      * @param LocalDate $start The start date, inclusive.
      * @param LocalDate $end   The end date, inclusive, validated as not before the start date.
      */
-    private function __construct(LocalDate $start, LocalDate $end)
-    {
-        $this->start = $start;
-        $this->end = $end;
+    private function __construct(
+        private readonly LocalDate $start,
+        private readonly LocalDate $end
+    ) {
     }
 
     /**
diff --git a/src/LocalDateTime.php b/src/LocalDateTime.php
index 6da9d614..76327045 100644
--- a/src/LocalDateTime.php
+++ b/src/LocalDateTime.php
@@ -24,14 +24,10 @@
  */
 final class LocalDateTime implements JsonSerializable, Stringable
 {
-    private readonly LocalDate $date;
-
-    private readonly LocalTime $time;
-
-    public function __construct(LocalDate $date, LocalTime $time)
-    {
-        $this->date = $date;
-        $this->time = $time;
+    public function __construct(
+        private readonly LocalDate $date,
+        private readonly LocalTime $time
+    ) {
     }
 
     /**
diff --git a/src/LocalTime.php b/src/LocalTime.php
index 9ca1e99b..e6aef2d4 100644
--- a/src/LocalTime.php
+++ b/src/LocalTime.php
@@ -43,26 +43,6 @@ final class LocalTime implements JsonSerializable, Stringable
     public const NANOS_PER_MILLI = 1_000_000;
     public const MILLIS_PER_SECOND = 1000;
 
-    /**
-     * The hour, in the range 0 to 23.
-     */
-    private readonly int $hour;
-
-    /**
-     * The minute, in the range 0 to 59.
-     */
-    private readonly int $minute;
-
-    /**
-     * The second, in the range 0 to 59.
-     */
-    private readonly int $second;
-
-    /**
-     * The nanosecond, in the range 0 to 999,999,999.
-     */
-    private readonly int $nano;
-
     /**
      * Private constructor. Use of() to obtain an instance.
      *
@@ -71,12 +51,12 @@ final class LocalTime implements JsonSerializable, Stringable
      * @param int $second The second-of-minute, validated in the range 0 to 59.
      * @param int $nano   The nano-of-second, validated in the range 0 to 999,999,999.
      */
-    private function __construct(int $hour, int $minute, int $second, int $nano)
-    {
-        $this->hour = $hour;
-        $this->minute = $minute;
-        $this->second = $second;
-        $this->nano = $nano;
+    private function __construct(
+        private readonly int $hour,
+        private readonly int $minute,
+        private readonly int $second,
+        private readonly int $nano
+    ) {
     }
 
     /**
diff --git a/src/MonthDay.php b/src/MonthDay.php
index 15912f92..fed9cdc8 100644
--- a/src/MonthDay.php
+++ b/src/MonthDay.php
@@ -16,26 +16,16 @@
  */
 final class MonthDay implements JsonSerializable, Stringable
 {
-    /**
-     * The month-of-year, from 1 to 12.
-     */
-    private readonly int $month;
-
-    /**
-     * The day-of-month, from 1 to 31.
-     */
-    private readonly int $day;
-
     /**
      * Private constructor. Use of() to obtain an instance.
      *
-     * @param int $month The month-of-year, validated.
-     * @param int $day   The day-of-month, validated.
+     * @param int $month The month-of-year, validated in the range of 1 to 12.
+     * @param int $day   The day-of-month, validated in the range of 1 to 31, valid for this month.
      */
-    private function __construct(int $month, int $day)
-    {
-        $this->month = $month;
-        $this->day = $day;
+    private function __construct(
+        private readonly int $month,
+        private readonly int $day
+    ) {
     }
 
     /**
diff --git a/src/Parser/PatternParser.php b/src/Parser/PatternParser.php
index 682819f3..e8f2c2a6 100644
--- a/src/Parser/PatternParser.php
+++ b/src/Parser/PatternParser.php
@@ -12,21 +12,14 @@
  */
 final class PatternParser implements DateTimeParser
 {
-    private readonly string $pattern;
-
-    /**
-     * @var string[]
-     */
-    private readonly array $fields;
-
     /**
      * @param string   $pattern The regular expression pattern.
      * @param string[] $fields  The fields constants to match.
      */
-    public function __construct(string $pattern, array $fields)
-    {
-        $this->pattern = $pattern;
-        $this->fields = $fields;
+    public function __construct(
+        private readonly string $pattern,
+        private readonly array $fields
+    ) {
     }
 
     public function getPattern(): string
diff --git a/src/Period.php b/src/Period.php
index 0f1844c9..6008c40e 100644
--- a/src/Period.php
+++ b/src/Period.php
@@ -19,12 +19,6 @@
  */
 final class Period implements JsonSerializable, Stringable
 {
-    private readonly int $years;
-
-    private readonly int $months;
-
-    private readonly int $days;
-
     /**
      * Private constructor. Use of() to obtain an instance.
      *
@@ -32,11 +26,11 @@ final class Period implements JsonSerializable, Stringable
      * @param int $months The number of months.
      * @param int $days   The number of days.
      */
-    private function __construct(int $years, int $months, int $days)
-    {
-        $this->years = $years;
-        $this->months = $months;
-        $this->days = $days;
+    private function __construct(
+        private readonly int $years,
+        private readonly int $months,
+        private readonly int $days
+    ) {
     }
 
     /**
diff --git a/src/TimeZoneOffset.php b/src/TimeZoneOffset.php
index ba1e2c53..26a5ff9a 100644
--- a/src/TimeZoneOffset.php
+++ b/src/TimeZoneOffset.php
@@ -15,8 +15,6 @@
  */
 final class TimeZoneOffset extends TimeZone
 {
-    private readonly int $totalSeconds;
-
     /**
      * The string representation of this time-zone offset.
      *
@@ -31,9 +29,8 @@ final class TimeZoneOffset extends TimeZone
      *
      * @param int $totalSeconds The total offset in seconds, validated from -64800 to +64800.
      */
-    private function __construct(int $totalSeconds)
+    private function __construct(private readonly int $totalSeconds)
     {
-        $this->totalSeconds = $totalSeconds;
     }
 
     /**
diff --git a/src/TimeZoneRegion.php b/src/TimeZoneRegion.php
index eb40b715..2324ab38 100644
--- a/src/TimeZoneRegion.php
+++ b/src/TimeZoneRegion.php
@@ -17,14 +17,11 @@
  */
 final class TimeZoneRegion extends TimeZone
 {
-    private readonly DateTimeZone $zone;
-
     /**
      * Private constructor. Use a factory method to obtain an instance.
      */
-    private function __construct(DateTimeZone $zone)
+    private function __construct(private readonly DateTimeZone $zone)
     {
-        $this->zone = $zone;
     }
 
     /**
diff --git a/src/Year.php b/src/Year.php
index 105278de..7125ce86 100644
--- a/src/Year.php
+++ b/src/Year.php
@@ -27,16 +27,10 @@ final class Year implements JsonSerializable, Stringable
     public const MAX_VALUE = LocalDate::MAX_YEAR;
 
     /**
-     * The year being represented.
+     * @param int $year The year, validated.
      */
-    private readonly int $year;
-
-    /**
-     * @param int $year The year to represent, validated.
-     */
-    private function __construct(int $year)
+    private function __construct(private readonly int $year)
     {
-        $this->year = $year;
     }
 
     /**
diff --git a/src/YearMonth.php b/src/YearMonth.php
index b30ff4a4..66a54f11 100644
--- a/src/YearMonth.php
+++ b/src/YearMonth.php
@@ -21,24 +21,14 @@
  */
 final class YearMonth implements JsonSerializable, Stringable
 {
-    /**
-     * The year, from MIN_YEAR to MAX_YEAR.
-     */
-    private readonly int $year;
-
-    /**
-     * The month, from 1 to 12.
-     */
-    private readonly int $month;
-
     /**
      * @param int $year  The year, validated from MIN_YEAR to MAX_YEAR.
      * @param int $month The month, validated in the range 1 to 12.
      */
-    private function __construct(int $year, int $month)
-    {
-        $this->year = $year;
-        $this->month = $month;
+    private function __construct(
+        private readonly int $year,
+        private readonly int $month
+    ) {
     }
 
     /**
diff --git a/src/YearMonthRange.php b/src/YearMonthRange.php
index 7606c982..24d077c8 100644
--- a/src/YearMonthRange.php
+++ b/src/YearMonthRange.php
@@ -24,24 +24,14 @@
  */
 class YearMonthRange implements IteratorAggregate, Countable, JsonSerializable, Stringable
 {
-    /**
-     * The start year-month, inclusive.
-     */
-    private readonly YearMonth $start;
-
-    /**
-     * The end year-month, inclusive.
-     */
-    private readonly YearMonth $end;
-
     /**
      * @param YearMonth $start The start year-month, inclusive.
      * @param YearMonth $end   The end year-month, inclusive, validated as not before the start year-month.
      */
-    private function __construct(YearMonth $start, YearMonth $end)
-    {
-        $this->start = $start;
-        $this->end = $end;
+    private function __construct(
+        private readonly YearMonth $start,
+        private readonly YearMonth $end
+    ) {
     }
 
     /**
diff --git a/src/YearWeek.php b/src/YearWeek.php
index f430775b..e7f68a5d 100644
--- a/src/YearWeek.php
+++ b/src/YearWeek.php
@@ -23,24 +23,14 @@
  */
 final class YearWeek implements JsonSerializable, Stringable
 {
-    /**
-     * The year, from MIN_YEAR to MAX_YEAR.
-     */
-    private readonly int $year;
-
-    /**
-     * The week number, from 1 to 53. Must be valid for the year.
-     */
-    private readonly int $week;
-
     /**
      * @param int $year The year, validated from MIN_YEAR to MAX_YEAR.
      * @param int $week The week number, validated in the range 1 to 53, and valid for the year.
      */
-    private function __construct(int $year, int $week)
-    {
-        $this->year = $year;
-        $this->week = $week;
+    private function __construct(
+        private readonly int $year,
+        private readonly int $week
+    ) {
     }
 
     /**
diff --git a/src/ZonedDateTime.php b/src/ZonedDateTime.php
index 86b9d646..41c4fb3a 100644
--- a/src/ZonedDateTime.php
+++ b/src/ZonedDateTime.php
@@ -24,38 +24,22 @@
  */
 class ZonedDateTime implements JsonSerializable, Stringable
 {
-    /**
-     * The local date-time.
-     */
-    private readonly LocalDateTime $localDateTime;
-
-    /**
-     * The time-zone offset from UTC/Greenwich.
-     */
-    private readonly TimeZoneOffset $timeZoneOffset;
-
-    /**
-     * The time-zone.
-     *
-     * It is either a TimeZoneRegion if this ZonedDateTime is region-based,
-     * or the same instance as the offset if this ZonedDateTime is offset-based.
-     */
-    private readonly TimeZone $timeZone;
-
-    /**
-     * The instant represented by this ZonedDateTime.
-     */
-    private readonly Instant $instant;
-
     /**
      * Private constructor. Use a factory method to obtain an instance.
-     */
-    private function __construct(LocalDateTime $localDateTime, TimeZoneOffset $offset, TimeZone $zone, Instant $instant)
-    {
-        $this->localDateTime = $localDateTime;
-        $this->timeZone = $zone;
-        $this->timeZoneOffset = $offset;
-        $this->instant = $instant;
+     *
+     * @param LocalDateTime  $localDateTime  The local date-time.
+     * @param TimeZoneOffset $timeZoneOffset The time-zone offset from UTC/Greenwich.
+     * @param TimeZone       $timeZone       The time-zone. It is either a TimeZoneRegion if this ZonedDateTime is
+     *                                       region-based, or the same instance as the offset if this ZonedDateTime
+     *                                       is offset-based.
+     * @param Instant        $instant        The instant represented by this ZonedDateTime.
+     */
+    private function __construct(
+        private readonly LocalDateTime $localDateTime,
+        private readonly TimeZoneOffset $timeZoneOffset,
+        private readonly TimeZone $timeZone,
+        private readonly Instant $instant
+    ) {
     }
 
     /**
diff --git a/tools/ecs/ecs.php b/tools/ecs/ecs.php
index a994f446..b3843ff5 100644
--- a/tools/ecs/ecs.php
+++ b/tools/ecs/ecs.php
@@ -80,6 +80,7 @@
 use SlevomatCodingStandard\Sniffs\Commenting\DocCommentSpacingSniff;
 use SlevomatCodingStandard\Sniffs\Namespaces\ReferenceUsedNamesOnlySniff;
 use SlevomatCodingStandard\Sniffs\Namespaces\UseSpacingSniff;
+use Symplify\CodingStandard\Fixer\Spacing\StandaloneLinePromotedPropertyFixer;
 use Symplify\EasyCodingStandard\Config\ECSConfig;
 use Symplify\EasyCodingStandard\ValueObject\Set\SetList;
 
@@ -193,6 +194,7 @@
             WhitespaceAfterCommaInArrayFixer::class,
             NoTrailingCommaInSinglelineArrayFixer::class,
             TrailingCommaInMultilineFixer::class,
+            StandaloneLinePromotedPropertyFixer::class,
         ]
     );