made Methods static

src/.editorconfig

@@ -2,3 +2,113 @@
 
 # Default severity for analyzer diagnostics with category 'Performance'
 dotnet_analyzer_diagnostic.category-Performance.severity = warning
+csharp_using_directive_placement = outside_namespace:silent
+csharp_prefer_simple_using_statement = true:suggestion
+csharp_prefer_braces = true:silent
+csharp_style_namespace_declarations = block_scoped:silent
+csharp_style_prefer_method_group_conversion = true:silent
+csharp_style_prefer_top_level_statements = true:silent
+csharp_style_expression_bodied_methods = false:silent
+
+[*.{cs,vb}]
+dotnet_style_operator_placement_when_wrapping = beginning_of_line
+tab_width = 4
+indent_size = 4
+[*.cs]
+#### Naming styles ####
+
+# Naming rules
+
+dotnet_naming_rule.private_or_internal_field_should_be_pascalcase_.severity = suggestion
+dotnet_naming_rule.private_or_internal_field_should_be_pascalcase_.symbols = private_or_internal_field
+dotnet_naming_rule.private_or_internal_field_should_be_pascalcase_.style = pascalcase_
+
+dotnet_naming_rule.private_or_internal_static_field_should_be_pascalcase_.severity = suggestion
+dotnet_naming_rule.private_or_internal_static_field_should_be_pascalcase_.symbols = private_or_internal_static_field
+dotnet_naming_rule.private_or_internal_static_field_should_be_pascalcase_.style = pascalcase_
+
+dotnet_naming_rule.private_method_should_be_pascalcase_.severity = suggestion
+dotnet_naming_rule.private_method_should_be_pascalcase_.symbols = private_method
+dotnet_naming_rule.private_method_should_be_pascalcase_.style = pascalcase_
+
+# Symbol specifications
+
+dotnet_naming_symbols.private_or_internal_field.applicable_kinds = field
+dotnet_naming_symbols.private_or_internal_field.applicable_accessibilities = internal, private, private_protected
+dotnet_naming_symbols.private_or_internal_field.required_modifiers = 
+
+dotnet_naming_symbols.private_or_internal_static_field.applicable_kinds = field
+dotnet_naming_symbols.private_or_internal_static_field.applicable_accessibilities = internal, private, private_protected
+dotnet_naming_symbols.private_or_internal_static_field.required_modifiers = static
+
+dotnet_naming_symbols.private_method.applicable_kinds = method
+dotnet_naming_symbols.private_method.applicable_accessibilities = private
+dotnet_naming_symbols.private_method.required_modifiers = 
+
+# Naming styles
+
+dotnet_naming_style.pascalcase_.required_prefix = 
+dotnet_naming_style.pascalcase_.required_suffix = _
+dotnet_naming_style.pascalcase_.word_separator = 
+dotnet_naming_style.pascalcase_.capitalization = pascal_case
+
+dotnet_naming_style.pascalcase_.required_prefix = 
+dotnet_naming_style.pascalcase_.required_suffix = _
+dotnet_naming_style.pascalcase_.word_separator = 
+dotnet_naming_style.pascalcase_.capitalization = pascal_case
+
+dotnet_naming_style.pascalcase_.required_prefix = 
+dotnet_naming_style.pascalcase_.required_suffix = _
+dotnet_naming_style.pascalcase_.word_separator = 
+dotnet_naming_style.pascalcase_.capitalization = pascal_case
+
+# CA1822: Mark members as static
+dotnet_diagnostic.CA1822.severity = warning
+
+[*.{cs,vb}]
+#### Naming styles ####
+
+# Naming rules
+
+dotnet_naming_rule.interface_should_be_begins_with_i.severity = suggestion
+dotnet_naming_rule.interface_should_be_begins_with_i.symbols = interface
+dotnet_naming_rule.interface_should_be_begins_with_i.style = begins_with_i
+
+dotnet_naming_rule.types_should_be_pascal_case.severity = suggestion
+dotnet_naming_rule.types_should_be_pascal_case.symbols = types
+dotnet_naming_rule.types_should_be_pascal_case.style = pascal_case
+
+dotnet_naming_rule.non_field_members_should_be_pascal_case.severity = suggestion
+dotnet_naming_rule.non_field_members_should_be_pascal_case.symbols = non_field_members
+dotnet_naming_rule.non_field_members_should_be_pascal_case.style = pascal_case
+
+# Symbol specifications
+
+dotnet_naming_symbols.interface.applicable_kinds = interface
+dotnet_naming_symbols.interface.applicable_accessibilities = public, internal, private, protected, protected_internal, private_protected
+dotnet_naming_symbols.interface.required_modifiers = 
+
+dotnet_naming_symbols.types.applicable_kinds = class, struct, interface, enum
+dotnet_naming_symbols.types.applicable_accessibilities = public, internal, private, protected, protected_internal, private_protected
+dotnet_naming_symbols.types.required_modifiers = 
+
+dotnet_naming_symbols.non_field_members.applicable_kinds = property, event, method
+dotnet_naming_symbols.non_field_members.applicable_accessibilities = public, internal, private, protected, protected_internal, private_protected
+dotnet_naming_symbols.non_field_members.required_modifiers = 
+
+# Naming styles
+
+dotnet_naming_style.begins_with_i.required_prefix = I
+dotnet_naming_style.begins_with_i.required_suffix = 
+dotnet_naming_style.begins_with_i.word_separator = 
+dotnet_naming_style.begins_with_i.capitalization = pascal_case
+
+dotnet_naming_style.pascal_case.required_prefix = 
+dotnet_naming_style.pascal_case.required_suffix = 
+dotnet_naming_style.pascal_case.word_separator = 
+dotnet_naming_style.pascal_case.capitalization = pascal_case
+
+dotnet_naming_style.pascal_case.required_prefix = 
+dotnet_naming_style.pascal_case.required_suffix = 
+dotnet_naming_style.pascal_case.word_separator = 
+dotnet_naming_style.pascal_case.capitalization = pascal_case

src/Ical.Net.CoreUnitTests/AlarmTest.cs

@@ -11,7 +11,7 @@ public class AlarmTest
     {
         private const string _tzid = "US-Eastern";
 
-        public void TestAlarm(string calendarString, List<IDateTime> dates, CalDateTime start, CalDateTime end)
+        public static void TestAlarm(string calendarString, List<IDateTime> dates, CalDateTime start, CalDateTime end)
         {
             var iCal = Calendar.Load(calendarString);
             ProgramTest.TestCal(iCal);

src/Ical.Net.CoreUnitTests/EqualityAndHashingTests.cs

@@ -438,7 +438,7 @@ public void CalDateTimeTests()
             Assert.AreNotEqual(asLocal, asUtc);
         }
 
-        private void TestComparison(Func<CalDateTime, IDateTime, bool> calOp, Func<int?, int?, bool> intOp)
+        private static void TestComparison(Func<CalDateTime, IDateTime, bool> calOp, Func<int?, int?, bool> intOp)
         {
             int? intSome = 1;
             int? intGreater = 2;

src/Ical.Net.CoreUnitTests/RecurrenceTests.cs

@@ -21,7 +21,7 @@ public class RecurrenceTests
     {
         private const string _tzid = "US-Eastern";
 
-        private void EventOccurrenceTest(
+        private static void EventOccurrenceTest(
             Calendar cal,
             IDateTime fromDate,
             IDateTime toDate,

src/Ical.Net/CalendarComponents/Alarm.cs

@@ -53,7 +53,7 @@ public string Summary
             set => Properties.Set("SUMMARY", value);
         }
 
-        public Trigger Trigger
+        public Trigger? Trigger
         {
             get => Properties.Get<Trigger>(TriggerRelation.Key);
             set => Properties.Set(TriggerRelation.Key, value);
@@ -91,7 +91,7 @@ public IList<AlarmOccurrence> GetOccurrences(IRecurringComponent rc, IDateTime f
                     fromDate = rc.Start.Copy<IDateTime>();
                 }
 
-                var d = default(TimeSpan);
+                TimeSpan? d = default;
                 foreach (var o in rc.GetOccurrences(fromDate, toDate))
                 {
                     var dt = o.Period.StartTime;
@@ -108,12 +108,12 @@ public IList<AlarmOccurrence> GetOccurrences(IRecurringComponent rc, IDateTime f
                         // Use the "last-found" duration as a reference point
                         else if (d != default)
                         {
-                            dt = o.Period.StartTime.Add(d);
+                            dt = o.Period.StartTime.Add(d.Value);
                         }
                         else
                         {
                             throw new ArgumentException(
-                                "Alarm trigger is relative to the START of the occurrence; however, the occurence has no discernible end.");
+                                "Alarm trigger is relative to the START of the occurrence; however, the occurrence has no discernible end.");
                         }
                     }
 

src/Ical.Net/CalendarComponents/CalendarComponent.cs

@@ -15,7 +15,7 @@ public class CalendarComponent : CalendarObject, ICalendarComponent
         /// </summary>
         public CalendarPropertyList Properties { get; protected set; }
 
-        public CalendarComponent() : base()
+        public CalendarComponent()
         {
             Initialize();
         }

src/Ical.Net/CalendarComponents/RecurringComponent.cs

@@ -31,7 +31,7 @@ public IList<Attachment> Attachments
             set => Properties.Set("ATTACH", value);
         }
 
-        /// <summary> AKA Tags; a List of <see cref="String"/> Category Names </summary>
+        /// <summary> AKA Tags; a List of <see cref="string"/> Category Names </summary>
         public IList<string> Categories
         {
             get => Properties.GetMany<string>("CATEGORIES");

src/Ical.Net/CalendarComponents/Todo.cs

@@ -157,7 +157,7 @@ public bool IsCompleted(IDateTime currDt)
                 // Evaluate to the previous occurrence.
                 _mEvaluator.EvaluateToPreviousOccurrence(Completed, currDt);
 
-                return _mEvaluator.Periods.Cast<Period>().All(p => !p.StartTime.GreaterThan(Completed) || !currDt.GreaterThanOrEqual(p.StartTime));
+                return _mEvaluator.Periods.All(p => !p.StartTime.GreaterThan(Completed) || !currDt.GreaterThanOrEqual(p.StartTime));
             }
             return false;
         }

src/Ical.Net/CalendarComponents/VTimeZone.cs

@@ -353,7 +353,7 @@ public override bool Equals(object obj)
         {
             if (ReferenceEquals(null, obj)) return false;
             if (ReferenceEquals(this, obj)) return true;
-            if (obj.GetType() != this.GetType()) return false;
+            if (obj.GetType() != GetType()) return false;
             return Equals((VTimeZone)obj);
         }
 

src/Ical.Net/Collections/GroupedList.cs

@@ -104,7 +104,7 @@ public void Clear()
             _lists.Clear();
         }
 
-        public bool ContainsKey(TGroup group) => _dictionary.ContainsKey(@group);
+        public bool ContainsKey(TGroup group) => _dictionary.ContainsKey(group);
 
         public int Count => _lists.Sum(list => list.Count);
 
@@ -114,8 +114,8 @@ public int CountOf(TGroup group) => _dictionary.ContainsKey(group)
 
         public IEnumerable<TItem> Values() => _dictionary.Values.SelectMany(i => i);
 
-        public IEnumerable<TItem> AllOf(TGroup group) => _dictionary.ContainsKey(@group)
-            ? (IEnumerable<TItem>) _dictionary[@group]
+        public IEnumerable<TItem> AllOf(TGroup group) => _dictionary.ContainsKey(group)
+            ? (IEnumerable<TItem>) _dictionary[group]
             : new TItem[0];
 
         public bool Remove(TItem obj)

src/Ical.Net/DataTypes/Period.cs

@@ -59,9 +59,9 @@ public override void CopyFrom(ICopyable obj)
 
         protected bool Equals(Period other) => Equals(StartTime, other.StartTime) && Equals(EndTime, other.EndTime) && Duration.Equals(other.Duration);
 
-        public override bool Equals(object obj)
+        public override bool Equals(object? obj)
         {
-            if (ReferenceEquals(null, obj)) return false;
+            if (obj is null) return false;
             if (ReferenceEquals(this, obj)) return true;
             return obj.GetType() == GetType() && Equals((Period) obj);
         }
@@ -85,17 +85,17 @@ public override string ToString()
 
         private void ExtrapolateTimes()
         {
-            if (EndTime == null && StartTime != null && Duration != default)
+            if (EndTime == null && StartTime != null && Duration != null)
             {
-                EndTime = StartTime.Add(Duration);
+                EndTime = StartTime.Add(Duration.Value);
             }
-            else if (Duration == default && StartTime != null && EndTime != null)
+            else if (Duration == null && StartTime != null && EndTime != null)
             {
                 Duration = EndTime.Subtract(StartTime);
             }
-            else if (StartTime == null && Duration != default && EndTime != null)
+            else if (StartTime == null && Duration != null && EndTime != null)
             {
-                StartTime = EndTime.Subtract(Duration);
+                StartTime = EndTime.Subtract(Duration.Value);
             }
         }
 
@@ -131,8 +131,8 @@ public IDateTime? EndTime
             }
         }
 
-        private TimeSpan _duration;
-        public TimeSpan Duration
+        private TimeSpan? _duration;
+        public TimeSpan? Duration
         {
             get
             {

src/Ical.Net/DataTypes/RecurrencePattern.cs

@@ -8,6 +8,35 @@
 
 namespace Ical.Net.DataTypes
 {
+
+    public static class XRecurrence
+    {
+        public static void IncrementDate(this RecurrencePattern pattern, ref DateTime dt) => pattern.IncrementDate_(ref dt, pattern.Interval);
+        public static void DecrementDate(this RecurrencePattern pattern, ref DateTime dt) => pattern.IncrementDate_(ref dt, -pattern.Interval);
+        static void IncrementDate_(this RecurrencePattern pattern, ref DateTime dt, int interval)
+        {
+            // FIXME: use a more specific exception.
+            if (interval == 0)
+            {
+                throw new Exception("Cannot evaluate with an interval of zero.  Please use an interval other than zero.");
+            }
+
+            var old = dt;
+            dt = pattern.Frequency switch
+            {
+                FrequencyType.Secondly => old.AddSeconds(interval),
+                FrequencyType.Minutely => old.AddMinutes(interval),
+                FrequencyType.Hourly => old.AddHours(interval),
+                FrequencyType.Daily => old.AddDays(interval),
+                FrequencyType.Weekly => old.AddWeeks(interval, pattern.FirstDayOfWeek),
+                FrequencyType.Monthly => old.AddDays(-old.Day + 1).AddMonths(interval),
+                FrequencyType.Yearly => old.AddDays(-old.DayOfYear + 1).AddYears(interval),
+                _ => throw new Exception(
+                    "FrequencyType.NONE cannot be evaluated. Please specify a FrequencyType before evaluating the recurrence.")
+            };
+        }
+
+    }
     /// <summary> An iCalendar representation of the <c>RRULE</c> property. https://tools.ietf.org/html/rfc5545#section-3.3.10 </summary>
     /// <remarks>
     /// Multiple Patterns are combined into a <see cref="CalendarComponents.CalendarEvent"/>

src/Ical.Net/Evaluation/Evaluator.cs

@@ -2,7 +2,6 @@
 using System.Collections.Generic;
 using System.Globalization;
 using Ical.Net.DataTypes;
-using Ical.Net.Utility;
 
 namespace Ical.Net.Evaluation
 {
@@ -41,36 +40,13 @@ private void Initialize()
             MPeriods = new HashSet<Period>();
         }
 
-        protected IDateTime ConvertToIDateTime(DateTime dt, IDateTime referenceDate)
+        protected static IDateTime ConvertToIDateTime(DateTime dt, IDateTime referenceDate)
         {
             IDateTime newDt = new CalDateTime(dt, referenceDate.TzId);
             newDt.AssociateWith(referenceDate);
             return newDt;
         }
 
-        protected void IncrementDate(RecurrencePattern pattern, ref DateTime dt, int interval)
-        {
-            // FIXME: use a more specific exception.
-            if (interval == 0)
-            {
-                throw new Exception("Cannot evaluate with an interval of zero.  Please use an interval other than zero.");
-            }
-
-            var old = dt;
-            dt = pattern.Frequency switch
-            {
-                FrequencyType.Secondly => old.AddSeconds(interval),
-                FrequencyType.Minutely => old.AddMinutes(interval),
-                FrequencyType.Hourly => old.AddHours(interval),
-                FrequencyType.Daily => old.AddDays(interval),
-                FrequencyType.Weekly => old.AddWeeks(interval, pattern.FirstDayOfWeek),
-                FrequencyType.Monthly => old.AddDays(-old.Day + 1).AddMonths(interval),
-                FrequencyType.Yearly => old.AddDays(-old.DayOfYear + 1).AddYears(interval),
-                _ => throw new Exception(
-                    "FrequencyType.NONE cannot be evaluated. Please specify a FrequencyType before evaluating the recurrence.")
-            };
-        }
-
         public System.Globalization.Calendar Calendar { get; private set; }
 
         public DateTime EvaluationStartBounds