ILSpy/ICSharpCode.Decompiler.Tests/TestCases/Pretty/FirstClassSpanConversions.cs

// Copyright (c) 2026 Siegfried Pammer
// 
// Permission is hereby granted, free of charge, to any person obtaining a copy of this
// software and associated documentation files (the "Software"), to deal in the Software
// without restriction, including without limitation the rights to use, copy, modify, merge,
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// to whom the Software is furnished to do so, subject to the following conditions:
// 
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// substantial portions of the Software.
// 
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// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
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using System;

namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
{
	internal static class FirstClassSpanConversions
	{
		internal class Base
		{
		}

		internal class Derived : Base
		{
		}

		internal class SpanConvertible
		{
			public static implicit operator ReadOnlySpan<int>(SpanConvertible c)
			{
				return default(ReadOnlySpan<int>);
			}
		}

		internal class DerivedSpanConvertible : SpanConvertible
		{
		}

		public static void AcceptReadOnlySpanChar(ReadOnlySpan<char> s)
		{
		}

		public static void AcceptReadOnlySpanBase(ReadOnlySpan<Base> s)
		{
		}

		public static void AcceptInReadOnlySpan(in ReadOnlySpan<int> s)
		{
		}

		public static void ObjectOrReadOnlySpanChar(object a)
		{
		}

		public static void ObjectOrReadOnlySpanChar(ReadOnlySpan<char> a)
		{
		}

		public static void StringArgument(string s)
		{
			AcceptReadOnlySpanChar(s);
			ObjectOrReadOnlySpanChar(s);
			s.ExtensionOnReadOnlySpanChar();
		}

		public static ReadOnlySpan<char> StringToReadOnlySpanCharReturn(string s)
		{
			return s;
		}

		public static int StringToReadOnlySpanCharLocal(string s)
		{
			// The local is read twice so it survives decompilation; a single-use span local is
			// inlined into its consumer by general decompiler policy, independent of this feature.
			ReadOnlySpan<char> readOnlySpan = s;
			return readOnlySpan.Length + readOnlySpan.Length;
		}

		public static void VarianceReadOnlySpan(ReadOnlySpan<Derived> s)
		{
			AcceptReadOnlySpanBase(s);
		}

		public static void VarianceSpan(Span<Derived> s)
		{
			AcceptReadOnlySpanBase(s);
		}

		public static ReadOnlySpan<Base> VarianceReturn(ReadOnlySpan<Derived> s)
		{
			return s;
		}

		public static void CovariantArrayToReadOnlySpan(Derived[] a)
		{
			AcceptReadOnlySpanBase(a);
		}

		public static ReadOnlySpan<Base> CovariantArrayThroughOperator(Derived[] a)
		{
			// ReadOnlySpan<Base>.op_Implicit(Base[]) applied to a Derived[]: array covariance
			// means the IL passes the argument without a cast instruction, and the span
			// conversion the call performs relates exactly these two types.
			return a;
		}

		public static ReadOnlySpan<int> UserDefinedOperatorToSpan(DerivedSpanConvertible c)
		{
			// The operator is declared on the base type, so the conversion is user-defined even
			// though its target is a span type. Only the user-defined conversion that resolves
			// to this very operator may be folded into the cast; a span conversion never applies
			// to a source type outside the language's own span-convertible set.
			return c;
		}

		public static void InArgument(int[] a)
		{
			AcceptInReadOnlySpan(a);
		}

		public static void ByValueOrIn(ReadOnlySpan<int> s)
		{
		}

		public static void ByValueOrIn(in ReadOnlySpan<int> s)
		{
		}

		public static void CallByValueOrIn(ReadOnlySpan<int> s, int[] a)
		{
			// Without 'in' the by-value overload is the better parameter-passing choice, also
			// through the span conversion; with 'in' only the in-overload binds, so the
			// keyword must survive decompilation.
			ByValueOrIn(s);
			ByValueOrIn(in s);
			ByValueOrIn(a);
		}
	}

	internal static class FirstClassSpanConversionsExtensions
	{
		public static void ExtensionOnReadOnlySpanChar(this ReadOnlySpan<char> s)
		{
		}
	}
}