fix: avoid byref delegate parameters incompatible with Mono/Xamarin (issue #458)

source/Handlebars.Test/ClosureBuilderTests.cs

@@ -123,7 +123,7 @@ private static List<DecoratorDelegate> GenerateDecoratorDelegates(ClosureBuilder
             var helpers = new List<DecoratorDelegate>();
             for (int i = 0; i < count; i++)
             {
-                DecoratorDelegate helper = (in EncodedTextWriter writer, BindingContext context, TemplateDelegate function) => function;
+                DecoratorDelegate helper = (EncodedTextWriter writer, BindingContext context, TemplateDelegate function) => function;
                 builder.Add(Const(helper));
                 helpers.Add(helper);
             }

source/Handlebars.Test/DecoratorTests.cs

@@ -46,7 +46,7 @@ public void OverrideFunctionWithDecorator(IHandlebars handlebars)
                 (TemplateDelegate function, in DecoratorOptions options, in Context context, in Arguments arguments) =>
                 {
                     var value = arguments.At<int>(0); 
-                    return (in EncodedTextWriter writer, BindingContext bindingContext) =>
+                    return (EncodedTextWriter writer, BindingContext bindingContext) =>
                     {
                         writer.WriteSafeString(value);
                         function(writer, bindingContext);

source/Handlebars.Test/IssueTests.cs

@@ -733,5 +733,32 @@ public void UnrecognisedExpressionThrowsOutOfMemoryException()
 
             Assert.Throws<HandlebarsCompilerException>(()=> Handlebars.Compile(source));
         }
+
+        // Issue: https://github.com/Handlebars-Net/Handlebars.Net/issues/458
+        // System.NotImplementedException: byref delegate on Xamarin.iOS / Mono
+        // The Mono runtime does not support delegates with byref (in/ref) parameters.
+        // TemplateDelegate previously used `in EncodedTextWriter` which produced a
+        // byref delegate incompatible with Mono's AOT/JIT compiler.
+        [Fact]
+        public void Issue458_BasicTemplateCompilationAndRender()
+        {
+            // Validates the scenario that fails on Mono: simple compile + render
+            var handlebars = Handlebars.Create();
+            var render = handlebars.Compile("{{input}}");
+            object data = new { input = 42 };
+            var actual = render(data);
+            Assert.Equal("42", actual);
+        }
+
+        // Issue: https://github.com/Handlebars-Net/Handlebars.Net/issues/458
+        // Ensures block helpers still work after the byref delegate fix
+        [Fact]
+        public void Issue458_BlockHelperTemplateCompilationAndRender()
+        {
+            var handlebars = Handlebars.Create();
+            var render = handlebars.Compile("{{#if show}}visible{{/if}}");
+            var actual = render(new { show = true });
+            Assert.Equal("visible", actual);
+        }
     }
 }

source/Handlebars/Compiler/CompilationContext.cs

@@ -9,7 +9,7 @@ public CompilationContext(ICompiledHandlebarsConfiguration configuration)
         {
             Configuration = configuration;
             BindingContext = Expression.Parameter(typeof(BindingContext), "context");
-            EncodedWriter = Expression.Parameter(typeof(EncodedTextWriter).MakeByRefType(), "writer");
+            EncodedWriter = Expression.Parameter(typeof(EncodedTextWriter), "writer");
 
             Args = new CompilationContextArgs(this);
         }
@@ -18,7 +18,7 @@ public CompilationContext(CompilationContext context)
         {
             Configuration = context.Configuration;
             BindingContext = Expression.Parameter(typeof(BindingContext), "context");
-            EncodedWriter = Expression.Parameter(typeof(EncodedTextWriter).MakeByRefType(), "writer");
+            EncodedWriter = Expression.Parameter(typeof(EncodedTextWriter), "writer");
 
             Args = new CompilationContextArgs(this);
         }

source/Handlebars/Compiler/FunctionBuilder.cs

@@ -10,8 +10,8 @@ namespace HandlebarsDotNet.Compiler
 {
     internal static class FunctionBuilder
     {
-        private static readonly TemplateDelegate EmptyTemplateLambda = 
-            (in EncodedTextWriter writer, BindingContext context) => { };
+        private static readonly TemplateDelegate EmptyTemplateLambda =
+            (EncodedTextWriter writer, BindingContext context) => { };
 
         public static Expression Reduce(Expression expression, CompilationContext context, out IReadOnlyList<DecoratorDefinition> decorators)
         {

source/Handlebars/Compiler/HandlebarsCompiler.cs

@@ -8,7 +8,7 @@
 
 namespace HandlebarsDotNet.Compiler
 {
-    public delegate void TemplateDelegate(in EncodedTextWriter writer, BindingContext context);
+    public delegate void TemplateDelegate(EncodedTextWriter writer, BindingContext context);
 
     internal static class HandlebarsCompiler
     {
@@ -29,7 +29,7 @@ public static TemplateDelegate Compile(ExtendedStringReader source, CompilationC
             {
                 var a1 = action;
                 var decorator = decorators.Compile(compilationContext);
-                action = (in EncodedTextWriter writer, BindingContext context) =>
+                action = (EncodedTextWriter writer, BindingContext context) =>
                 {
                     decorator(writer, context, a1)(writer, context);
                 };
@@ -63,7 +63,7 @@ internal static TemplateDelegate CompileView(ViewReaderFactory readerFactoryFact
             {
                 var a1 = compiledView;
                 var decorator = decorators.Compile(compilationContext);
-                compiledView = (in EncodedTextWriter writer, BindingContext context) =>
+                compiledView = (EncodedTextWriter writer, BindingContext context) =>
                 {
                     decorator(writer, context, a1)(writer, context);
                 };
@@ -78,7 +78,7 @@ internal static TemplateDelegate CompileView(ViewReaderFactory readerFactoryFact
 
             var compiledLayout = CompileView(readerFactoryFactory, layoutPath, new CompilationContext(compilationContext));
 
-            return (in EncodedTextWriter writer, BindingContext context) =>
+            return (EncodedTextWriter writer, BindingContext context) =>
             {
                 var config = context.Configuration;
                 using var bindingContext = BindingContext.Create(config, null);

source/Handlebars/Compiler/Translation/Expression/DecoratorDefinition.cs

@@ -4,7 +4,7 @@
 
 namespace HandlebarsDotNet.Compiler
 {
-    public delegate TemplateDelegate DecoratorDelegate(in EncodedTextWriter writer, BindingContext context, TemplateDelegate function);
+    public delegate TemplateDelegate DecoratorDelegate(EncodedTextWriter writer, BindingContext context, TemplateDelegate function);
 
     internal readonly struct DecoratorDefinition
     {
@@ -20,7 +20,7 @@ public DecoratorDefinition(Expression decorator, ExpressionContainer<TemplateDel
 
         public DecoratorDelegate Compile(CompilationContext context)
         {
-            if (Function is null || Decorator is null) return (in EncodedTextWriter writer, BindingContext bindingContext, TemplateDelegate function) => function;
+            if (Function is null || Decorator is null) return (EncodedTextWriter writer, BindingContext bindingContext, TemplateDelegate function) => function;
 
             var lambda = Expression.Lambda<DecoratorDelegate>(
                 Decorator, 
@@ -47,7 +47,7 @@ CompilationContext context
                 var definition = decoratorDefinitions[index];
                 var f = definition.Compile(context);
                 var current = decorator;
-                decorator = (in EncodedTextWriter writer, BindingContext bindingContext, TemplateDelegate function) => 
+                decorator = (EncodedTextWriter writer, BindingContext bindingContext, TemplateDelegate function) =>
                     f(writer, bindingContext, current(writer, bindingContext, function));
             }