Uses the keyword 'in' for read-only types only

Author: NikolayPianikov

Immutype.Benchmark/RecordWithFourProperties.cs

@@ -7,7 +7,7 @@ namespace Immutype.Benchmark
     public record PersonRecordWithFourProperties(string? Name, int Age, string? LastName, bool HasPassport);
 
     [Immutype.Target]
-    public record struct PersonRecordStructWithFourProperties(string? Name, int Age, string? LastName, bool HasPassport);
+    public readonly record struct PersonRecordStructWithFourProperties(string? Name, int Age, string? LastName, bool HasPassport);
 
     [MemoryDiagnoser]
     [Orderer(SummaryOrderPolicy.FastestToSlowest)]

Immutype.Benchmark/RecordWithOneProperty.cs

@@ -7,7 +7,7 @@ namespace Immutype.Benchmark
     public record PersonRecordWithOneProperty(string? Name);
 
     [Immutype.Target]
-    public record struct PersonRecordStructWithOneProperty(string? Name);
+    public readonly record struct PersonRecordStructWithOneProperty(string? Name);
 
     [MemoryDiagnoser]
     [Orderer(SummaryOrderPolicy.FastestToSlowest)]

Immutype.Benchmark/RecordWithTwoProperties.cs

@@ -7,7 +7,7 @@ namespace Immutype.Benchmark
     public record PersonRecordWithTwoProperties(string? Name, int Age);
 
     [Immutype.Target]
-    public record struct PersonRecordStructWithTwoProperties(string? Name, int Age);
+    public readonly record struct PersonRecordStructWithTwoProperties(string? Name, int Age);
 
     [MemoryDiagnoser]
     [Orderer(SummaryOrderPolicy.FastestToSlowest)]

Immutype.UsageScenarios.Tests/ApplyingDefaults.cs

@@ -14,7 +14,7 @@ namespace Immutype.UsageScenarios.Tests.ApplyingDefaults
     // $description=Applying defaults
     // {
     [Immutype.Target]
-    internal record Person(string Name = "John", int Age = 17);
+    internal readonly record struct Person(string Name = "John", int Age = 17);
 
     public class ApplyingDefaults
     {

Immutype.UsageScenarios.Tests/Array.cs

@@ -14,7 +14,7 @@ namespace Immutype.UsageScenarios.Tests.Array
     // $description=Array
     // {
     [Immutype.Target]
-    internal record Person(string Name, int Age = 0, params Person[] Friends);
+    internal readonly record struct Person(string Name, int Age = 0, params Person[] Friends);
 
     public class Array
     { 

Immutype.UsageScenarios.Tests/Removing.cs

@@ -14,7 +14,7 @@ namespace Immutype.UsageScenarios.Tests.Removing
     // $description=Removing
     // {
     [Immutype.Target]
-    internal record Person(
+    internal readonly record struct Person(
         string Name,
         int Age = 0,
         params Person[] Friends);

Immutype/Core/ISyntaxNodeFactory.cs

@@ -7,6 +7,8 @@ namespace Immutype.Core
     internal interface ISyntaxNodeFactory
     {
         bool IsValueType(TypeDeclarationSyntax typeDeclarationSyntax);
+        
+        bool IsReadonlyType(TypeDeclarationSyntax typeDeclarationSyntax);
 
         bool HasTargetAttribute(MemberDeclarationSyntax memberDeclarationSyntax);
 

Immutype/Core/MethodsFactory.cs

@@ -25,7 +25,9 @@ public IEnumerable<MemberDeclarationSyntax> Create(GenerationContext<TypeDeclara
                 .WithType(targetType)
                 .AddModifiers(SyntaxFactory.Token(SyntaxKind.ThisKeyword));
 
-            if (context.Options is CSharpParseOptions { LanguageVersion: >= LanguageVersion.CSharp7_2 } && _syntaxNodeFactory.IsValueType(context.Syntax))
+            if (
+                context.Options is CSharpParseOptions { LanguageVersion: >= LanguageVersion.CSharp7_2 }
+                && _syntaxNodeFactory.IsReadonlyType(context.Syntax))
             {
                 thisParameter = thisParameter.AddModifiers(SyntaxFactory.Token(SyntaxKind.InKeyword));
             }

Immutype/Core/SyntaxNodeFactory.cs

@@ -36,6 +36,9 @@ public bool IsValueType(TypeDeclarationSyntax typeDeclarationSyntax) =>
                 _ => false
             };
 
+        public bool IsReadonlyType(TypeDeclarationSyntax typeDeclarationSyntax) =>
+            typeDeclarationSyntax.Modifiers.Any(i => i.IsKind(SyntaxKind.ReadOnlyKeyword));
+
         public bool HasTargetAttribute(MemberDeclarationSyntax memberDeclarationSyntax) =>
             memberDeclarationSyntax.AttributeLists
                 .SelectMany(i => i.Attributes)