Some PR feedback.

src/Draco.Compiler/Internal/Codegen/MetadataCodegen.cs

@@ -522,7 +522,7 @@ private void EncodeModule(IModule module, TypeDefinitionHandle? parent, ref int
         ++procIndex;
 
         // We encode every class
-        foreach (var @class in module.Types.Values)
+        foreach (var @class in module.Classes.Values)
         {
             this.EncodeClass(@class, parent: createdModule, fieldIndex: ref fieldIndex, procIndex: ref procIndex);
         }

src/Draco.Compiler/Internal/OptimizingIr/Model/IClass.cs

@@ -3,6 +3,9 @@
 
 namespace Draco.Compiler.Internal.OptimizingIr.Model;
 
+/// <summary>
+/// Read-only interface if a <see cref="Class"/>
+/// </summary>
 internal interface IClass
 {
     /// <summary>

src/Draco.Compiler/Internal/OptimizingIr/Model/IModule.cs

@@ -49,9 +49,9 @@ internal interface IModule
     public IReadOnlyDictionary<FunctionSymbol, IProcedure> Procedures { get; }
 
     /// <summary>
-    /// The compiled types within this module.
+    /// The compiled classes within this module.
     /// </summary>
-    public IReadOnlyDictionary<TypeSymbol, IClass> Types { get; }
+    public IReadOnlyDictionary<TypeSymbol, IClass> Classes { get; }
 
     /// <summary>
     /// The procedure performing global initialization.

src/Draco.Compiler/Internal/OptimizingIr/Model/Module.cs

@@ -19,7 +19,7 @@ internal sealed class Module : IModule
     IReadOnlyDictionary<ModuleSymbol, IModule> IModule.Submodules => this.submodules;
 
     public IDictionary<TypeSymbol, IClass> Types => this.types;
-    IReadOnlyDictionary<TypeSymbol, IClass> IModule.Types => this.types;
+    IReadOnlyDictionary<TypeSymbol, IClass> IModule.Classes => this.types;
 
     public IReadOnlySet<FieldSymbol> Fields => this.fields;
     public IReadOnlySet<PropertySymbol> Properties => this.properties;

src/Draco.Compiler/Internal/OptimizingIr/Model/Procedure.cs

@@ -50,11 +50,10 @@ public Procedure(Module declaringModule, Class? declaringType, FunctionSymbol sy
 
     public int GetParameterIndex(ParameterSymbol symbol)
     {
-        if (symbol is SourceThisParameterSymbol) return 0;
-        var isStaticMethod = symbol.ContainingSymbol.IsStatic;
+        if (symbol.IsThis) return 0;
         var idx = this.Symbol.Parameters.IndexOf(symbol);
         if (idx == -1) throw new System.ArgumentOutOfRangeException(nameof(symbol));
-        return isStaticMethod ? idx : idx + 1;
+        return symbol.ContainingSymbol.IsStatic ? idx : idx + 1;
     }
 
     public BasicBlock DefineBasicBlock(LabelSymbol symbol)

src/Draco.Compiler/Internal/Symbols/Error/ErrorThisParameterSymbol.cs

@@ -1,6 +1,11 @@
 namespace Draco.Compiler.Internal.Symbols.Error;
 
-internal class ErrorThisParameterSymbol(TypeSymbol type, FunctionSymbol containingSymbol) : ParameterSymbol
+/// <summary>
+/// An error this parameter symbol.
+/// </summary>
+/// <param name="type"></param>
+/// <param name="containingSymbol"></param>
+internal sealed class ErrorThisParameterSymbol(TypeSymbol type, FunctionSymbol containingSymbol) : ParameterSymbol
 {
     public override TypeSymbol Type { get; } = type;
     public override FunctionSymbol ContainingSymbol { get; } = containingSymbol;

src/Draco.Compiler/Internal/Symbols/FunctionSymbol.cs

@@ -78,7 +78,7 @@ public delegate IOperand CodegenDelegate(
     /// <summary>
     /// The receiver of this function, if it has one.
     /// </summary>
-    public TypeSymbol? Receiver => this.IsStatic
+    public TypeSymbol? ReceiverType => this.IsStatic
         ? null
         : this.ContainingSymbol as TypeSymbol;
 

src/Draco.Compiler/Internal/Symbols/ParameterSymbol.cs

@@ -18,6 +18,8 @@ internal abstract partial class ParameterSymbol : LocalSymbol
     public virtual bool IsVariadic => false;
 
     public override bool IsMutable => false;
+
+    public virtual bool IsThis => false;
     // NOTE: Override for covariant return type
     public override ParameterSymbol? GenericDefinition => null;
     public override SymbolKind Kind => SymbolKind.Parameter;

src/Draco.Compiler/Internal/Symbols/Source/SourceThisParameterSymbol.cs

@@ -9,6 +9,7 @@ internal sealed class SourceThisParameterSymbol(FunctionSymbol containingSymbol,
     public override string Name => "this";
     public override FunctionSymbol ContainingSymbol { get; } = containingSymbol;
     public override bool IsVariadic => false;
+    public override bool IsThis => true;
     public override ThisParameterSyntax DeclaringSyntax { get; } = syntax;
 
     public override ImmutableArray<AttributeInstance> Attributes => [];