refactor: null check and readonly props and fields

src/dscom.test/builder/DynamicBuilder.cs

@@ -27,15 +27,22 @@ public DynamicBuilder(string name)
 
     public T WithCustomAttribute(Type type, Type[]? constructorParamTypes, object[]? values)
     {
-        var dispIDAttributeConstructor = type.GetConstructor(constructorParamTypes ?? Array.Empty<Type>()) ?? throw new ArgumentException($"Constructor for {type} not found");
+        var dispIDAttributeConstructor = type.GetConstructor(constructorParamTypes ?? Array.Empty<Type>());
+        if (dispIDAttributeConstructor == null)
+        {
+            throw new ArgumentException($"Constructor for {type} not found");
+        }
 
         var attributeUsageAttribute = type.GetCustomAttribute<AttributeUsageAttribute>();
-        if (attributeUsageAttribute != null && !attributeUsageAttribute.ValidOn.HasFlag(AttributeTarget))
+        if (attributeUsageAttribute != null)
         {
-            throw new ArgumentException($"Attribute {type.Name} not allowed here.");
+            if (!attributeUsageAttribute.ValidOn.HasFlag(AttributeTarget))
+            {
+                throw new ArgumentException($"Attribute {type.Name} not allowed here.");
+            }
         }
 
-        var dispIDAttributeBuilder = new CustomAttributeBuilder(dispIDAttributeConstructor, values ?? Array.Empty<object>());
+        var dispIDAttributeBuilder = new CustomAttributeBuilder(dispIDAttributeConstructor!, values ?? Array.Empty<object>());
         CustomAttributeBuilder.Add(dispIDAttributeBuilder);
         return (T)this;
     }

src/dscom.test/builder/DynamicEnumBuilder.cs

@@ -47,7 +47,12 @@ public DynamicEnumBuilder WithLiteralAndAttribute(string name, object? value, Ty
     {
         WithLiteral(name, value);
 
-        var attributeConstructor = type.GetConstructor(constructorParamTypes ?? Array.Empty<Type>()) ?? throw new ArgumentException($"Constructor for {type} not found");
+        var attributeConstructor = type.GetConstructor(constructorParamTypes ?? Array.Empty<Type>());
+        if (attributeConstructor == null)
+        {
+            throw new ArgumentException($"Constructor for {type} not found");
+        }
+
         var attributeUsageAttribute = type.GetCustomAttribute<AttributeUsageAttribute>();
         if (attributeUsageAttribute != null)
         {

src/dscom/RegistrationServices.cs

@@ -141,8 +141,13 @@ public void RegisterTypeForComClients(Type type, ref Guid g)
     /// <exception cref="T:System.ArgumentNullException">The <paramref name="type" /> parameter cannot be created.</exception>
     public int RegisterTypeForComClients(Type type, ComTypes.RegistrationClassContext classContext, ComTypes.RegistrationConnectionType flags)
     {
-        var value = (type.GetCustomAttributes<GuidAttribute>().FirstOrDefault()?.Value
-                    ?? type.Assembly.GetCustomAttributes<GuidAttribute>().FirstOrDefault()?.Value) ?? throw new ArgumentException($"The given type {type} does not have a valid GUID attribute.");
+        var value = type.GetCustomAttributes<GuidAttribute>().FirstOrDefault()?.Value
+                    ?? type.Assembly.GetCustomAttributes<GuidAttribute>().FirstOrDefault()?.Value;
+        if (value == null)
+        {
+            throw new ArgumentException($"The given type {type} does not have a valid GUID attribute.");
+        }
+
         var guid = new Guid(value);
 
         var genericClassFactory = typeof(ClassFactory<>);
@@ -189,7 +194,12 @@ public bool RegisterAssembly(Assembly assembly, bool registerCodeBase, ManagedCa
             throw new ArgumentException("Cannot register a ReflectionOnly or dynamic assembly");
         }
 
-        var fullName = assembly.FullName ?? throw new ArgumentException("Cannot register an assembly without a full name");
+        var fullName = assembly.FullName;
+        if (fullName is null)
+        {
+            throw new ArgumentException("Cannot register an assembly without a full name");
+        }
+
         string? codeBase = null;
         if (registerCodeBase && assembly.Location is null)
         {

src/dscom/TypeInfoResolver.cs

@@ -86,7 +86,11 @@ public TypeInfoResolver(WriterContext writerContext)
                 MajorVersion = 2,
                 MinorVersion = 0
             };
-            var typeLibOle = GetTypeLibFromIdentifier(identifierOle) ?? throw new COMException("System.Guid not found in any type library");
+            var typeLibOle = GetTypeLibFromIdentifier(identifierOle);
+            if (typeLibOle == null)
+            {
+                throw new COMException("System.Guid not found in any type library");
+            }
             typeLibOle.GetTypeInfo(0, out retval);
         }
         else if (type.GUID == new Guid(Guids.IID_IDispatch))

src/dscom/TypeLibIdentifier.cs

@@ -53,7 +53,7 @@ public struct TypeLibIdentifier
     /// </summary>
     /// <param name="obj"></param>
     /// <returns></returns>
-    public override readonly bool Equals(object? obj)
+    public override bool Equals(object? obj)
     {
         return obj is TypeLibIdentifier o && Equals(o);
     }
@@ -63,7 +63,7 @@ public struct TypeLibIdentifier
     /// </summary>
     /// <param name="other">The <see cref="TypeLibIdentifier"/> to compare</param>
     /// <returns>true if the specified object is equal to the current object; otherwise, false.</returns>
-    public readonly bool Equals(TypeLibIdentifier other)
+    public bool Equals(TypeLibIdentifier other)
     {
         return MajorVersion == other.MajorVersion
                 && MinorVersion == other.MinorVersion
@@ -75,7 +75,7 @@ public struct TypeLibIdentifier
     /// A hash code for the current object.
     /// </summary>
     /// <returns>A hash code for the current object.</returns>
-    public override readonly int GetHashCode()
+    public override int GetHashCode()
     {
         return MajorVersion.GetHashCode() ^ MinorVersion.GetHashCode() ^ LibID.GetHashCode() ^ LanguageIdentifier.GetHashCode();
     }

src/dscom/internal/structs/CUSTDATA.cs

@@ -18,7 +18,7 @@ public struct CUSTDATA
 
     public IntPtr prgCustData;
 
-    public readonly CUSTDATAITEM[] Items
+    public CUSTDATAITEM[] Items
     {
         get
         {

src/dscom/internal/structs/HRESULT.cs

@@ -18,9 +18,9 @@ public struct HRESULT
     [FieldOffset(0)]
     private readonly int _value;
 
-    public readonly bool Succeeded => _value >= 0;
+    public bool Succeeded => _value >= 0;
 
-    public readonly bool Failed => _value < 0;
+    public bool Failed => _value < 0;
 
     public HRESULT(int i)
     {
@@ -78,15 +78,15 @@ public HRESULT(int i)
     }
 
     [SecurityCritical, SecuritySafeCritical]
-    public readonly void ThrowIfFailed(string? message = null)
+    public void ThrowIfFailed(string? message = null)
     {
         if (Failed)
         {
             throw new COMException(message, Marshal.GetExceptionForHR(_value));
         }
     }
 
-    public override readonly bool Equals(object? obj)
+    public override bool Equals(object? obj)
     {
         if (obj == null)
         {
@@ -111,7 +111,7 @@ public HRESULT(int i)
         return false;
     }
 
-    public override readonly int GetHashCode()
+    public override int GetHashCode()
     {
         return _value;
     }

src/dscom/writer/ClassWriter.cs

@@ -122,7 +122,11 @@ public override void CreateTypeInheritance()
         {
             foreach (var interfaceTypeValue in sourceInterfaceAttribute.Value.Split('\0').Distinct())
             {
-                var interfaceType = SourceType.Assembly.GetType(interfaceTypeValue) ?? AppDomain.CurrentDomain.GetAssemblies().Select(z => z.GetType(interfaceTypeValue)).FirstOrDefault(x => x != null);
+                var interfaceType = SourceType.Assembly.GetType(interfaceTypeValue);
+                if (interfaceType == null)
+                {
+                    interfaceType = AppDomain.CurrentDomain.GetAssemblies().Select(z => z.GetType(interfaceTypeValue)).FirstOrDefault(x => x != null);
+                }
                 if (interfaceType != null)
                 {
                     var interfaceTypeInfo = Context.TypeInfoResolver.ResolveTypeInfo(interfaceType);