{"id":5073,"date":"2022-06-26T20:16:36","date_gmt":"2022-06-26T18:16:36","guid":{"rendered":"https:\/\/soci.hu\/blog\/?p=5073"},"modified":"2022-06-26T20:16:36","modified_gmt":"2022-06-26T18:16:36","slug":"is-compiling-c-10-code-for-net-4-7-possible","status":"publish","type":"post","link":"https:\/\/soci.hu\/blog\/index.php\/2022\/06\/26\/is-compiling-c-10-code-for-net-4-7-possible\/","title":{"rendered":"Is compiling C# 10 code for .NET 4.7 possible?"},"content":{"rendered":"\n

I have asked this question today. Yes, it is possible. Here is the proof:<\/p>\n\n\n

\nusing System;\nusing System.Linq;\nusing System.Runtime.CompilerServices;\n\n\/\/C# 10\nnamespace ConsoleApp1;\n\ninternal class Program\n{\n    static void Main(string[] args)\n    {\n        Console.WriteLine("Hello C# 10");\n        CallerArgumentExpressionDemo(args.Length == 0 && (args.FirstOrDefault() ?? "42") == "42");\n\n        int x = 0;\n        \/\/C# 10 - Assignment and declaration in same deconstruction\n        (x, string y) = new DemoStructRecord(2,"apple");\n        Console.WriteLine($"{x}, {y}");\n    }\n\n    \/\/C# 10 - CallerArgumentExpression\n    public static void CallerArgumentExpressionDemo(bool b, [CallerArgumentExpression("b")] string message = null)\n    {\n        if (b)\n        {\n            Console.WriteLine($"Message from the caller expression: {message}");\n        }\n    }\n}\n\n\/\/C# 10 - record struct\nrecord struct DemoStructRecord(int A, string B)\n{\n    private const string SomeConstant = "Something";\n\n    \/\/C# 10 - Interpolated string constant\n    private const string InterpolatedConstant = $"This is an interpolated constant {SomeConstant}";\n\n    public readonly override string ToString()\n    {\n        return $"{nameof(A)}: {A}, {nameof(B)}: {B}";\n    }\n}\n\nrecord DemoRecord(int A, string B)\n{\n    \/\/C# 10 - sealed ToString\n    public sealed override string ToString()\n    {\n        return $"{nameof(A)}: {A}, {nameof(B)}: {B}";\n    }\n}\n\npublic readonly struct Measurement\n{\n    \/\/C# 10 - parameterless ctor in struct\n    public Measurement()\n    {\n        Value = double.NaN;\n        Description = "Undefined";\n    }\n\n    public Measurement(double value, string description)\n    {\n        Value = value;\n        Description = description;\n    }\n\n    \/\/C# 9 (init only props)\n    public double Value { get; init; }\n    public string Description { get; init; }\n\n    public override string ToString() => $"{Value} ({Description})";\n}\n<\/pre><\/div>\n\n\n
As you see, I packed several C#9 and 10 features into the code, and they compile happily. There were two tricky points, however. CallerArgumentExpression is not defined in .NET Framework; you have to add it to your program:<\/p>\n\n\n
\nnamespace System.Runtime.CompilerServices;\n\n[AttributeUsage(AttributeTargets.Parameter, AllowMultiple = false, Inherited = false)]\ninternal sealed class CallerArgumentExpressionAttribute : Attribute\n{\n    public CallerArgumentExpressionAttribute(string parameterName)\n    {\n        ParameterName = parameterName;\n    }\n\n    public string ParameterName { get; }\n}\n<\/pre><\/div>\n\n\n
The other problematic feature is init-only properties. To be able to compile your code to .NET 4.7, you have to define it yourself:<\/p>\n\n\n
\nnamespace System.Runtime.CompilerServices\n{\n    internal static class IsExternalInit { }\n}\n<\/pre><\/div>\n\n\n
For completeness, here is the project file:<\/p>\n\n\n
\n<?xml version="1.0" encoding="utf-8"?>\n<Project ToolsVersion="15.0" xmlns="http:\/\/schemas.microsoft.com\/developer\/msbuild\/2003">\n  <Import Project="$(MSBuildExtensionsPath)\\$(MSBuildToolsVersion)\\Microsoft.Common.props" Condition="Exists('$(MSBuildExtensionsPath)\\$(MSBuildToolsVersion)\\Microsoft.Common.props')" \/>\n  <PropertyGroup>\n    <Configuration Condition=" '$(Configuration)' == '' ">Debug<\/Configuration>\n    <Platform Condition=" '$(Platform)' == '' ">AnyCPU<\/Platform>\n    <LangVersion>10.0<\/LangVersion>\n    <ProjectGuid>{AFFA1FD0-4D9D-4801-B66C-26F232D32B3D}<\/ProjectGuid>\n    <OutputType>Exe<\/OutputType>\n    <RootNamespace>ConsoleApp1<\/RootNamespace>\n    <AssemblyName>ConsoleApp1<\/AssemblyName>\n    <TargetFrameworkVersion>v4.7<\/TargetFrameworkVersion>\n    <FileAlignment>512<\/FileAlignment>\n    <AutoGenerateBindingRedirects>true<\/AutoGenerateBindingRedirects>\n    <Deterministic>true<\/Deterministic>\n  <\/PropertyGroup>\n  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">\n    <PlatformTarget>AnyCPU<\/PlatformTarget>\n    <DebugSymbols>true<\/DebugSymbols>\n    <DebugType>full<\/DebugType>\n    <Optimize>false<\/Optimize>\n    <OutputPath>bin\\Debug\\<\/OutputPath>\n    <DefineConstants>DEBUG;TRACE<\/DefineConstants>\n    <ErrorReport>prompt<\/ErrorReport>\n    <WarningLevel>4<\/WarningLevel>\n  <\/PropertyGroup>\n  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">\n    <PlatformTarget>AnyCPU<\/PlatformTarget>\n    <DebugType>pdbonly<\/DebugType>\n    <Optimize>true<\/Optimize>\n    <OutputPath>bin\\Release\\<\/OutputPath>\n    <DefineConstants>TRACE<\/DefineConstants>\n    <ErrorReport>prompt<\/ErrorReport>\n    <WarningLevel>4<\/WarningLevel>\n  <\/PropertyGroup>\n  <ItemGroup>\n    <Reference Include="System" \/>\n    <Reference Include="System.Core" \/>\n    <Reference Include="System.Xml.Linq" \/>\n    <Reference Include="System.Data.DataSetExtensions" \/>\n    <Reference Include="Microsoft.CSharp" \/>\n    <Reference Include="System.Data" \/>\n    <Reference Include="System.Net.Http" \/>\n    <Reference Include="System.Xml" \/>\n  <\/ItemGroup>\n  <ItemGroup>\n    <Compile Include="CallerArgumentExpressionAttribute.cs" \/>\n    <Compile Include="IsExternalInit.cs" \/>\n    <Compile Include="Program.cs" \/>\n    <Compile Include="Properties\\AssemblyInfo.cs" \/>\n  <\/ItemGroup>\n  <Import Project="$(MSBuildToolsPath)\\Microsoft.CSharp.targets" \/>\n<\/Project>\n<\/pre><\/div>\n\n\n
I intentionally used the old project file format for this demo. It is useful to convert older projects to the new SDK format; however, it needs extensive testing, so we cannot schedule it for a while.<\/p>\n\n\n\n
(For a nuget package, if the target is an SDK project or the older project with package references, nuget won’t copy nuget content to the destination project; it only links to the files. This design decision has many severe implications, but I don’t diverge more in this article.)<\/p>\n\n\n\n
Here is the output of the running code:<\/p>\n\n\n\n
\"\"<\/figure>\n\n\n\n
It’s interesting to see how the CallerArgumentExpressionAttribute works. It nicely receives the argument C# expression.<\/p>\n\n\n\n
To make sure I compiled for .NET 4.7, I decompiled the output assembly by DotPeak:<\/p>\n\n\n\n
\"\"
It is compiled for .NET 4.7<\/figcaption><\/figure>\n","protected":false},"excerpt":{"rendered":"
I have asked this question today. Yes, it is possible. Here is the proof: As you see, I packed several C#9 and…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[8,170,10,4],"tags":[],"class_list":["post-5073","post","type-post","status-publish","format-standard","hentry","category-net","category-dotnet-troubleshooting","category-c","category-szakmai-elet"],"_links":{"self":[{"href":"https:\/\/soci.hu\/blog\/index.php\/wp-json\/wp\/v2\/posts\/5073","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/soci.hu\/blog\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/soci.hu\/blog\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/soci.hu\/blog\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/soci.hu\/blog\/index.php\/wp-json\/wp\/v2\/comments?post=5073"}],"version-history":[{"count":4,"href":"https:\/\/soci.hu\/blog\/index.php\/wp-json\/wp\/v2\/posts\/5073\/revisions"}],"predecessor-version":[{"id":5142,"href":"https:\/\/soci.hu\/blog\/index.php\/wp-json\/wp\/v2\/posts\/5073\/revisions\/5142"}],"wp:attachment":[{"href":"https:\/\/soci.hu\/blog\/index.php\/wp-json\/wp\/v2\/media?parent=5073"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/soci.hu\/blog\/index.php\/wp-json\/wp\/v2\/categories?post=5073"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/soci.hu\/blog\/index.php\/wp-json\/wp\/v2\/tags?post=5073"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}