fix: avoid byref delegate parameters incompatible with Mono/Xamarin (issue #458)#627
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…o/Xamarin (#458) Mono's AOT/JIT compiler does not support delegates with byref parameters (ref/in). TemplateDelegate and DecoratorDelegate used `in EncodedTextWriter` which caused System.NotImplementedException: byref delegate at runtime on Xamarin.iOS and other Mono-based platforms. - Change `TemplateDelegate` from `delegate void TemplateDelegate(in EncodedTextWriter, ...)` to pass the struct by value - Change `DecoratorDelegate` similarly - Update `CompilationContext.EncodedWriter` to use `typeof(EncodedTextWriter)` instead of `MakeByRefType()` so Expression.Lambda<TemplateDelegate> no longer generates a byref parameter - Update all lambda literals in HandlebarsCompiler, FunctionBuilder, DecoratorDefinition and tests to drop the `in` modifier EncodedTextWriter is a small readonly struct (3 reference-type fields) so the by-value copy is cheap and there is no observable behaviour change on standard .NET runtimes. Adds two regression tests: Issue458_BasicTemplateCompilationAndRender and Issue458_BlockHelperTemplateCompilationAndRender. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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Fixes #458
Root Cause
Mono's AOT/JIT compiler (used by Xamarin.iOS and other Mono-based platforms) does not support delegates whose parameter list includes byref types (
ref/in/out). Theinkeyword on a value-type parameter compiles to a managed byref, so any delegate type that usesinis a "byref delegate."In v2, two internal delegate types gained
in EncodedTextWriterparameters:TemplateDelegate—delegate void TemplateDelegate(in EncodedTextWriter writer, BindingContext context)DecoratorDelegate—delegate TemplateDelegate DecoratorDelegate(in EncodedTextWriter writer, ...)CompilationContextalso created the writer parameter astypeof(EncodedTextWriter).MakeByRefType(), so everyExpression.Lambda<TemplateDelegate>call produced a byref delegate, throwingSystem.NotImplementedException: byref delegateat template-compile time on Mono.Fix
Remove the
inmodifier from the two delegate type definitions soEncodedTextWriteris passed by value instead of by readonly reference:TemplateDelegate→delegate void TemplateDelegate(EncodedTextWriter writer, BindingContext context)DecoratorDelegate→delegate TemplateDelegate DecoratorDelegate(EncodedTextWriter writer, ...)CompilationContext.EncodedWriter→Expression.Parameter(typeof(EncodedTextWriter), "writer")EncodedTextWriteris a smallreadonly structcontaining three managed-reference fields (~24 bytes on 64-bit). Passing it by value incurs a negligible copy and produces no observable behaviour difference on standard .NET runtimes.The same
in-removal is applied to all lambda literals that match these delegate types, and to the two affected test helpers.Tests
Two regression tests added to
IssueTests.cs:Issue458_BasicTemplateCompilationAndRender— compile and render{{input}}Issue458_BlockHelperTemplateCompilationAndRender— compile and render{{#if show}}visible{{/if}}All 1748 existing tests continue to pass.
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