Now that we have enum constraint, why doesn&#39;t compiler allow me to write this code?

    public static TResult? ToEnum&lt;TResult&gt;(this String value, TResult? defaultValue)
        where TResult : Enum
    {
        return String.IsNullOrEmpty(value) ? defaultValue : (TResult?)Enum.Parse(typeof(TResult), value);
    }

The compiler says:

&gt; Error CS0453 The type &#39;TResult&#39; must be a non-nullable value type in order to use it as parameter &#39;T&#39; in the generic type or method &#39;Nullable&lt;T&gt;&#39;



C# 7.3 Enum constraint: Why can&#39;t I use the nullable enum?

I&#39;ve been looking at [Roslyn][1] for quite some time now, and I&#39;m curious and excited about it. One thing I noticed is that they mentioned that the compiler is re-written in managed code. This raises the question of whether Roslyn is able to run on non-.NET virtual machines, such as [Mono][2].

I would *really* love to embed C# scripting using Roslyn in my video games, and to use many of their other features in my applications, but I&#39;m wondering if using Roslyn will break the ability for it to run on Mono.

Has anyone tried running Roslyn on Mono? Is it possible? Why or why not?

To clarify, I&#39;m interested in both whether the managed assembly can run on Mono, and whether it can generate assemblies that mono can run.

  [1]: https://en.wikipedia.org/wiki/.NET_Compiler_Platform
  [2]: http://en.wikipedia.org/wiki/Mono_%28software%29


Is Roslyn cross platform?

When operations were introduced in Roslyn one of the goals was to provide lowered operations (I think it was in design review meeting video) which as far as I understand should provide explicit operations for implicit compiler actions on high level ones. I see Lowering directory in Roslyn, but classes are internal there. It is possible to get lowered operations now or no public API available yet?

In sample below operations already removing some implicit parts - adding return statement for expression body and expose symbol for overloaded operator. But pre and post increments differs only by kind.

    using Microsoft.CodeAnalysis;
    using Microsoft.CodeAnalysis.CSharp;
    using Microsoft.CodeAnalysis.CSharp.Syntax;
    using Microsoft.CodeAnalysis.Semantics;
    using System.Linq;
    
    namespace so39468373
    {
        internal static class Program
        {
            private static void Main()
            {
                var tree = CSharpSyntaxTree.ParseText(@&quot;
    public class c
    {
        public static c operator ++(c o) { return o; }
        static c pre(c o) =&gt; ++o;
        static c post(c o) =&gt; o++;
        public static void Main() {}
    }&quot;);
                var mscorlib = MetadataReference.CreateFromFile(typeof(object).Assembly.Location);
                var compilation = CSharpCompilation.Create(null, new[] { tree }, new[] { mscorlib });
                var model = compilation.GetSemanticModel(tree);
                foreach (var node in tree.GetRoot().DescendantNodes().OfType&lt;ArrowExpressionClauseSyntax&gt;())
                {
                    var operation = model.GetOperation(node);
                    var block = (IBlockStatement)operation;
                    var statement = (IReturnStatement)block.Statements.First();
                    var increment = (IIncrementExpression)statement.ReturnedValue;
                    // How to get lowered operations for increment here?
                }
            }
        }
    }

Code on github - https://github.com/isanych/so-39468373

Lowered operations in roslyn

I am trying to run  Asp.net MVC project retrieved from TFS source control. I have added all assembly references and I am able to build and compile successfully without any error or warning.

But I get the following error in the browser:

&gt; Could not find a part of the path
&gt; &#39;C:\B8akWorkspace\B8akProject\B8akSolution\B8AK.Portal\bin\roslyn\csc.exe&#39;.

Here is a full screenshot of the error page.

[![enter image description here][1]][1]

After few days of research, I understood that [Roslyn][2] is .Net compiler platform that offers advance compiling features. However, I do not understand why my build is trying to find \bin\roslyn\csc.exe because I did not configure anything related to Roslyn nor I intend to use Roslyn in my project.


  [1]: http://i.stack.imgur.com/lkxJP.png
  [2]: https://roslyn.codeplex.com/

Could not find a part of the path ... bin\roslyn\csc.exe

In Visual Studio 2015 or later, I can open the &#39;C# interactive window&#39;, and run code:

    &gt; 5 + 3
    8

That&#39;s cute. Now how can I interact *my code*—my classes? Assume I have a project open.

    &gt; new Cog()
    (1,5): error CS0246: The type or namespace name &#39;Cog&#39; could not be found (are you missing a using directive or an assembly reference?)

Can the C# interactive window interact with my code?

I looked at the source code at http://referencesource.microsoft.com/, and it appears all the source code is in C#.

I also looked at the source code for the new C# compiler platform ([Roslyn][1]), and it is also in C#. How is that possible? Is C# language compiler written in C#? Or am I missing something obvious? If C# compiler is written in C# then how does it work?

  [1]: https://en.wikipedia.org/wiki/.NET_Compiler_Platform


In which language is the C# compiler written?

I am testing Visual Studio 2015 with C# 6.0 but the language features are not working. In an MVC web application, the following code does compile:

    if (!string.IsNullOrWhiteSpace(Model.Profile?.TypeName))
    {
        // More logic here...
    }

However, when I run the application via Debug and IIS Express, I get the following error:

&gt; CS1525: Invalid expression term &#39;.&#39;

How do I enable these features?

C# 6.0 Features Not Working with Visual Studio 2015

I was writing a unit test on a piece of code that returned JSON. The type that it returns is an anonymous type, so I thought to verify the values on it I&#39;d just cast the object to a `dynamic` to do my assertions.

However, when I do that, my build fails but I don&#39;t have any error messages. I was able to reproduce this with very simple code in a new Unit Test Project:

    [TestMethod]
    public void TestMethod1()
    {
        var obj = new { someValue = true };

        dynamic asDynamic = obj;

        Assert.IsTrue(asDynamic.someValue);
    }

See below for a screenshot of the build failing

[![build failing][1]][1]

The build succeeds when I comment out the assertion though:

[![build succeeding without assert][2]][2]

In contrast, I ran the following code in LinqPad 5 beta (which uses the Roslyn compiler) and had no issues:

    var obj = new { someValue = true };
    dynamic asDynamic = obj;
    Console.WriteLine((asDynamic.someValue == true).ToString());

&gt;True

What&#39;s going on here? Since the error isn&#39;t showing I can&#39;t tell if I&#39;m using `dynamic` incorrectly, or if it can&#39;t find the overload to use for `IsTrue()` because of the `dynamic`, or if this is a bug in the compiler (though I highly doubt this, I don&#39;t have any evidence that there&#39;s something wrong with my code).

Regarding the overload issue, I tried `Assert.IsTrue((bool)asDynamic.someValue);` but the build still fails, still no error message.

Per @RonBeyer&#39;s comment, I had also tried more casting such as below to no avail:

        dynamic asDynamic = (dynamic)obj;
        Assert.IsTrue(((dynamic)asDynamic).someValue);

        Assert.IsTrue((bool)asDynamic.somevalue);

Upon closer inspection, I found that there was an error listed in the Output window:


&gt; c:\...\DynamicBuildFailTest\UnitTest1.cs(16,33,16,42): error CS0656: Missing compiler required member &#39;Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfo.Create&#39;

Okay, VS2013 is better at reporting the errors, I will search based on those:

[![enter image description here][3]][3]

Okay, [adding a reference to Microsoft.CSharp fixed the build error](https://stackoverflow.com/a/13568247/526704), but I will leave this question open because it&#39;s presumably an issue with VS2015 that (in my mind) should be resolved.

  [1]: http://i.stack.imgur.com/pxQnz.png
  [2]: http://i.stack.imgur.com/PYKCt.png
  [3]: http://i.stack.imgur.com/TClxn.png

VS2015 build fails with no error message with Dynamic

I&#39;ve been taking a look to [Roslyn CTP][1] and, while it solves a similar problem to the [Expression tree API][2], both are immutable but Roslyn does so in a quite different way: 

* `Expression` nodes have no reference to the parent node, are modified using a `ExpressionVisitor` and that&#39;s why big parts can be reused. 

* Roslyn&#39;s `SyntaxNode`, on the other side, has a reference to its parent, so all the nodes effectively become a block that&#39;s impossible to re-use. Methods like `Update`, `ReplaceNode`, etc, are provided to make modifications. 

Where does this end? `Document`? `Project`? `ISolution`? The API promotes a step-by-step change of the tree (instead of a button up), but does each step makes a full copy?

Why they did they make such a choice? Is there some interesting trick I&#39;m missing? 


  [1]: http://msdn.microsoft.com/en-us/roslyn
  [2]: http://msdn.microsoft.com/en-us/library/bb397951.aspx

Are Roslyn SyntaxNodes reused?

In C# 6, you can use the [`nameof()`][1] operator to get a string containing the name of a variable or a type.

Is this evaluated at compile-time, or at runtime via some Roslyn API?

  [1]: https://msdn.microsoft.com/en-us/library/dn986596.aspx

Is nameof() evaluated at compile-time?

From a [press release][1] yesterday on InfoWorld regarding the new [Microsoft Roslyn][2]:

&gt; The most obvious advantage of this kind of &quot;deconstructed&quot; compiler is
&gt; that it allows the entire compile-execute process to be invoked from
&gt; within .Net applications. Hejlsberg demonstrated a C# program that
&gt; passed a few code snippets to the C# compiler as strings; the compiler
&gt; returned the resulting IL assembly code as an object, which was then
&gt; passed to the Common Language Runtime (CLR) for execution. Voil&#224;! With
&gt; Roslyn, C# gains a dynamic language&#39;s ability to generate and invoke
&gt; code at runtime.

I&#39;ve been able to do this since the release of .NET 4 with [`CSharpCodeProvider.CompileAssemblyFromSource`][3] which I in fact use in an ASP.Net project written awhile ago that does exactly that - allows a user to type in code into a textbox, choose assemblies/namespaces to reference, and then execute and display the output from that code on-the-fly for live environment code testing on Windows Azure.

Is `CodeDom` part of / a precurser to Roslyn?  What&#39;s the special benefit of Roslyn over `CodeDom`?


  [1]: http://www.infoworld.com/d/application-development/microsofts-roslyn-reinventing-the-compiler-we-know-it-176671
  [2]: http://www.microsoft.com/download/en/details.aspx?id=27746
  [3]: http://msdn.microsoft.com/en-us/library/system.codedom.compiler.codedomprovider.compileassemblyfromsource.aspx

Microsoft Roslyn vs. CodeDom

I want to use C# 6 in my project (null propagation, other features).

I&#39;ve installed VS 2015 on my PC and it works brilliantly and builds test code like

    var user = new SingleUserModel(); //all model fields are null
	var test = user.User?.Avatar?[&quot;blah&quot;];
But when I push my project to the repo and CI starts to build it, build fails because of unsupported `?`.

I&#39;ve installed VS2015 on CI server too but looke like it doesn&#39;t use it.
What can I do?

CI - CruiseControl .NET
Builds with `C:\Windows\Microsoft.NET\Framework\v4.0.30319\MSBuild.exe`

How to upgrade msbuild to C# 6?

I modified the example that comes with the new version of Roslyn that was released yesterday to use dynamic and ExpandoObject but I am getting a compiler error which I am not sure how to fix. The error is:

&gt; (7,21): error CS0656: Missing compiler required member &#39;Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfo.Create&#39;

Can you not use dynamics in the new compiler yet? How can I fix this? Here is the example that I updated:

    [TestMethod]
    public void EndToEndCompileAndRun()
    {
        var text = @&quot;using System.Dynamic;
        public class Calculator
        {
            public static object Evaluate()
            {
                dynamic x = new ExpandoObject();
                x.Result = 42;
                return x.Result;
            } 
        }&quot;;
    
        var tree = SyntaxFactory.ParseSyntaxTree(text);
        var compilation = CSharpCompilation.Create(
            &quot;calc.dll&quot;,
            options: new CSharpCompilationOptions(OutputKind.DynamicallyLinkedLibrary),
            syntaxTrees: new[] {tree},
            references: new[] {new MetadataFileReference(typeof (object).Assembly.Location), new MetadataFileReference(typeof (ExpandoObject).Assembly.Location)});
    
        Assembly compiledAssembly;
        using (var stream = new MemoryStream())
        {
            var compileResult = compilation.Emit(stream);
            compiledAssembly = Assembly.Load(stream.GetBuffer());
        }
    
        Type calculator = compiledAssembly.GetType(&quot;Calculator&quot;);
        MethodInfo evaluate = calculator.GetMethod(&quot;Evaluate&quot;);
        string answer = evaluate.Invoke(null, null).ToString();
    
        Assert.AreEqual(&quot;42&quot;, answer);
    }

Using System.Dynamic in Roslyn

After I have migrated my project from VS2013 to VS2015 the project no longer builds.  A compilation error occurs in the following LINQ statement:

    static void Main(string[] args)
    {
        decimal a, b;
        IEnumerable&lt;dynamic&gt; array = new string[] { &quot;10&quot;, &quot;20&quot;, &quot;30&quot; };
        var result = (from v in array
                      where decimal.TryParse(v, out a) &amp;&amp; decimal.TryParse(&quot;15&quot;, out b) &amp;&amp; a &lt;= b // Error here
                      orderby decimal.Parse(v)
                      select v).ToArray();
    }

The compiler returns an error:

&gt; Error CS0165  Use of unassigned local variable &#39;b&#39;

What causes this issue?  Is it possible to fix it through a compiler setting?

Roslyn failed to compile code

I am trying to create web application using Visual Studio 2015 and .NET 4.5.1.
When I publish the website, visual studio create folder named `roslyn`.

[![enter image description here][1]][1]

I know it&#39;s used to compile code on the fly, but unfortunately my hosting provider doesn&#39;t allow me to execute the compiler on their server.

How to publish the website without `roslyn` like previous version of Visual Studio?

EDIT:
I got this error when trying to acces my website.

[![enter image description here][2]][2]

It seems IIS trying to execute `roslyn\csc.exe` but my user account doesn&#39;t have permission to do that. With previous version of Visual Studio, this error doesn&#39;t show up.

  [1]: http://i.stack.imgur.com/s5UTs.png
  [2]: http://i.stack.imgur.com/QeBoa.png

Publish website without roslyn

Let’s consider this very simple async method:
	
	static async Task myMethodAsync() 
	{
		await Task.Delay(500);
	}

When I compile this with VS2013 (pre Roslyn compiler) the generated state-machine is a struct. 

	private struct &lt;myMethodAsync&gt;d__0 : IAsyncStateMachine
	{  
		...
	    void IAsyncStateMachine.MoveNext()
	    {
			...
	    }
	}

When I compile it with VS2015  (Roslyn) the generated code is this:

	private sealed class &lt;myMethodAsync&gt;d__1 : IAsyncStateMachine
	{
		...
		void IAsyncStateMachine.MoveNext()
		{
			...
		}
	}

As you can see Roslyn generates a class (and not a struct). If I remember correctly the first implementations of the async/await support in the old compiler (CTP2012 i guess) also generated classes and then it was changed to struct from performance reasons. (in some cases you can completely avoid boxing and heap allocation…) (See [this][1])

Does anyone know why this was changed again in Roslyn? (I don’t have any problem regarding this, I know that this change is transparent and does not change the behavior of any code, I’m just curious) 


  [1]: https://stackoverflow.com/questions/23609110/why-are-awaiters-async-await-structs-and-not-classes-can-classes-be-used

**Edit:**

The answer from @Damien_The_Unbeliever (and the source code :) ) imho explains everything. The described behaviour of Roslyn only applies for debug build (and that&#39;s needed because of the CLR limitation mentioned in the comment). In Release it also generates a struct (with all the benefits of that..). So this seems to be a very clever solution to support both Edit and Continue and better performance in production. Interesting stuff, thanks for everyone who participated! 

Why are async state machines classes (and not structs) in Roslyn?

There are a bunch of [related questions](https://stackoverflow.com/search?q=bin+roslyn) on this, though most of the answers _define_ Roslyn and/or provide a &quot;fix&quot; to some issue (`exe`, with hosting providers, etc.)

What I can&#39;t seem to track down is the &quot;why&quot; and &quot;what for&quot; (perhaps only in the context of ASP.Net MVC/Web API) in `/bin/roslyn`.

I ran in to similar issues (hosting - `.exe` restrictions, support for `4.6`, etc.) and my &quot;fix&quot; was to _&quot;just deploy to Azure&quot;_ (of course everything works without a hitch). But really, this doesn&#39;t answer:

- &lt;strike&gt;why are they needed?&lt;/strike&gt;
- does this mean that the they are used for `runtime` compilation &lt;strike&gt;(my brain  points to this, but that is a complete guess/my perhaps wrong grok), as [this SO post shows](https://stackoverflow.com/q/32282880/304683)&lt;/strike&gt; - unless corrected, this is &quot;it&quot; (more below).
- it seems &quot;removing the package&quot; is a &quot;fix&quot; [(based on some past answers)](https://stackoverflow.com/a/32295103/304683), &lt;strike&gt;but if so, it (re)begs the question&lt;/strike&gt;

I think _understanding_ this will help - e.g. I can&#39;t be the only one who will have an eyebrow raised seeing an `.exe` &quot;needed&quot;....

---
Update
--

Goes to show that &quot;hidden gems&quot; exist :) I&#39;ve [read this over and over](http://blogs.msdn.com/b/webdev/archive/2014/05/12/enabling-the-net-compiler-platform-roslyn-in-asp-net-applications.aspx)...after all it&#39;s been there for some time now -  &lt;strike&gt;but **_not_** the comments thread&lt;/strike&gt; - the original referenced link, circa 2014, has been redesigned by Microsoft and the comments are no longer displayed...luckily the relevant parts are below. 

BIG mistake - it was staring at me all this time (or at least since this exchange):

&gt; _Dmitry Dzygin 2 Jun 2015 12:53 AM_
&gt; 
&gt; _I have tried the latest version of the NuGet package, but there&#39;s seem to be a difference in the way the compiler is loaded/executed._
&gt; 
&gt; _In the v0.2.0.0 the Roslyn compiler would be loaded into memory, improving greatly performance for not pre-compiled websites with
&gt; multiple *.as*x/*.cshtml files. The new version, however, features a
&gt; new `/bin/roslyn/csc.exe` file, which is executed once per file,
&gt; completely removing the mentioned above optimization feature....._

Gold:

&gt; _XMao 2 Jun 2015 1:22 PM_
&gt; 
&gt; _@Dmitry The job of the `csc.exe` in `/bin/Roslyn` is to invoke the `VBCSCompiler.exe`, which sits in the same folder. `VBCSCompiler.exe`
&gt; is the process that does the actual compilation work. If the
&gt; VBCSCompiler is already running csc.exe will reuse it and thus we will
&gt; still gain the mentioned performance improvement._

Hth...

---
Update: 10/2017
--

Seems this is relevant after all this time so a further update. 

The [answer below by @Donny V](https://stackoverflow.com/a/38309167/304683) is an _option_. By fully compiling your application, including all `Views` (`.cshtml`/`.vbhtml`), you wouldn&#39;t need that `exe` in your application.

This is true even if Visual Studio (to this day, VS 2017, confusingly) will _still_ create the `/bin/roslyn` and it&#39;s contents in the `Publish` process, **even if &quot;full compile&quot; is set**.

You can test this by _excluding_ the `/bin/roslyn` folder and it&#39;s contents when pushing your application to your hosting provider. 

**Caveat**: 

As mentioned, fully compiling your application means you&#39;ll have to recompile it, even for `View` level changes.

What / why is Roslyn &quot;needed&quot; in /bin folder of Asp.Net

I&#39;m building a set of code diagnostics using Roslyn (in VS2015 Preview). Ideally, I&#39;d like any errors they produce to act as persistent errors, just as if I were violating a normal language rule.

There are a bunch of options, but I&#39;m having a hard time getting any of them to work consistently. I&#39;ve managed to implement a rudimentary syntax node action, i.e. one registered with 

    context.RegisterSyntaxNodeAction(AnalyzeSyntaxNode, SyntaxKind.InvocationExpression);

in the `Initialize` method of my diagnostic class. Lo and behold, when I open up a file which violates this diagnostic (while running the VSIX project), VS2015 shows an error:

- Red squiggle under the right bit of code
- Red block in the margin
- Error in the error list

However, the error goes away when I close the file.

I&#39;ve tried using `context.RegisterCompilationEndAction` as well, but this has two problems:

- It seems to fire inconsistently. *Usually* when I open the solution it fires, but not always. It doesn&#39;t fire on a clean/rebuild, which seems odd.
- Although diagnostics created *directly* in the analysis method fire, in order to implement the diagnostics I&#39;m using a visitor, like this - which may be inept:

        private static void AnalyzeEndCompilation(CompilationEndAnalysisContext context)
        {
            foreach (var tree in context.Compilation.SyntaxTrees)
            {
                var visitor = new ReportingVisitor(context.Compilation.GetSemanticModel(tree));
                visitor.Visit(tree.GetRoot());
                foreach (var diagnostic in visitor.Diagnostics)
                {
                    context.ReportDiagnostic(diagnostic);
                }
            }
        }

 I know that the diagnostics are being created - a breakpoint on the `ReportDiagnostic` line is hit several times - but I&#39;m not seeing anything in the error list. (Whereas a similar `ReportDiagnostic` call at the start of the method, or one per syntax tree with the file path, *does* get shown.)

What am I doing wrong here? The first approach (a syntax node action) would be ideal if feasible - it gives me exactly the context I need. Is there some setting in the project properties that I need to make the compiler use that for &quot;full project&quot; compilation as well as just interactive &quot;in the IDE&quot; handling? Is this perhaps just a bit of Roslyn integration which isn&#39;t quite finished yet?

(I can include the full code for the class if it would be useful - in this case I suspect it would be more noise than signal though.)

How can I make my code diagnostic syntax node action work on closed files?

In Visual Studio 2013, I used the Code Analysis window to provide reports to both the Development and Management teams.

[![Code Analysis window in Visual Studio 2013][1]][1]

In Visual Studio 2015 Enterprise RTM, these errors have returned to the error window and I can no longer just see CA issues for a single project, or filter them by type.

Is there a way to bring the Code Analysis window back? 

  [1]: http://i.stack.imgur.com/5aeI7.png

Where has the Code Analysis window gone?

I am facing a strange issue from roslyn compiler. Sometimes when I build the solution I face a strange issue in error list which does not let me build the solution. Here is the error:

&gt;Severity	Code	Description	Project	File	Line	Suppression State
Error		Unable to copy file &quot;D:\Sealogical New Website\SealogicalWebsite\packages\Microsoft.Net.Compilers.1.0.0\tools\csc.exe&quot; to &quot;bin\roslyn\csc.exe&quot;. Access to the path &#39;bin\roslyn\csc.exe&#39; is denied.	SealogicalWebsite			

&gt;Severity	Code	Description	Project	File	Line	Suppression State
Error		Unable to copy file &quot;D:\Sealogical New Website\SealogicalWebsite\packages\Microsoft.Net.Compilers.1.0.0\tools\VBCSCompiler.exe&quot; to &quot;bin\roslyn\VBCSCompiler.exe&quot;. Access to the path &#39;bin\roslyn\VBCSCompiler.exe&#39; is denied.	SealogicalWebsite	

 1. I try to clean the solution and rebuild it but does not work again.
    
 2. Tried to delete files manually but again shows an error pointing out
    I do not have right permissions to do this:
    
 3. Tried deleting from `CMD` but again shows the same error:

[![Image when trying to delete files manually][1]][1]

The only way to delete roslyn generated files is by restarting the PC and when restarted I can delete them manually without a problem.

I am administrator in my PC so there is no problem with that I guess.

This problem seems to happen in Visual Studi0 2015 and Visual Studio 2017.

I dont like restarting the PC 4-5 times a day or more thats why I am asking here.

Some other details:

 - I am the one who created this project so theoretically it should not
   be a problem to do this action.
   
 - When the project first created I did run the Visual Studion in
   Administrator Mode as I am doing now.
 - I am using ASP.MVC 5 template in my project.
 - Files which do not get deleted are `bin/roslyn/csc` and `bin/roslyn/VBCSCompiler`.

I could find a solution to remove this part from web.config so it does not generate those files:


    &lt;compilers&gt;
      &lt;compiler language=&quot;c#;cs;csharp&quot; extension=&quot;.cs&quot; type=&quot;Microsoft.CodeDom.Providers.DotNetCompilerPlatform.CSharpCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35&quot; warningLevel=&quot;4&quot; compilerOptions=&quot;/langversion:6 /nowarn:1659;1699;1701&quot; /&gt;
      &lt;compiler language=&quot;vb;vbs;visualbasic;vbscript&quot; extension=&quot;.vb&quot; type=&quot;Microsoft.CodeDom.Providers.DotNetCompilerPlatform.VBCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35&quot; warningLevel=&quot;4&quot; compilerOptions=&quot;/langversion:14 /nowarn:41008 /define:_MYTYPE=\&amp;quot;Web\&amp;quot; /optionInfer+&quot; /&gt;
    &lt;/compilers&gt;

But this solution would cause problem with new c# 6 features so I can not remove this section.....

Furthermore I tried this command in CMD to see if there is a process locking this file but anyway it did not show me any process at all:

    C:\WINDOWS\system32&gt;tasklist /m D:\SealogicalNewWebsite\SealogicalWebsite\SealogicalWebsite\bin\roslyn\csc.exe
    INFO: No tasks are running which match the specified criteria.

Does anybody knows a way how to handle this strange issue ?


  [1]: https://i.stack.imgur.com/XUcwF.png

Can not delete \bin\roslyn\VBCSCompiler.exe - Access is denied

While trying out the Visual Studio 2015 RC, I received a run-time error on previously working code.  Given the lambda  `(x =&gt; x.CustomerStatusID == CustomerStatuses.Active)` which was passed to a function as an `Expression&lt;&gt;`, the debugger shows a difference in the expression tree.  Formerly it compiled as this:

    .Lambda #Lambda1&lt;System.Func`2[Services.DataClasses.CustomerDC,System.Boolean]&gt;(Services.DataClasses.CustomerDC $x)
    {
        (System.Int32)$x.CustomerStatusID == 0
    }

But in C# 6.0 it now compiles as 

    .Lambda #Lambda1&lt;System.Func`2[Services.DataClasses.CustomerDC,System.Boolean]&gt;(Services.DataClasses.CustomerDC $x)
    {
        (System.Int32)$x.CustomerStatusID == (System.Int32).Constant&lt;Services.DataClasses.CustomerStatuses&gt;(Active)
    }

Although the fix to my tree-traversing code was straightforward and the additional detail is appreciated, does anyone know of any other gotchas floating around like this?  

Alternately, does anyone have a link to information on the specifics of how overload resolution was improved?  I cannot find any.

Enums in lambda expressions are compiled differently; consequence of overload resolution improvements?

I have this very simple example:

    class Program
    {
        class A
        {
            public bool B;
        }

        static void Main()
        {
            System.Collections.ArrayList list = null;

            if (list?.Count &gt; 0)
            {
                System.Console.WriteLine(&quot;Contains elements&quot;);
            }

            A a = null;

            if (a?.B)
            {
                System.Console.WriteLine(&quot;Is initialized&quot;);
            }
        }
    }

The line `if (list?.Count &gt; 0)` compiles perfectly which means that if `list` is `null`, the expression `Count &gt; 0` becomes `false` by default.

However, the line `if (a?.B)` throws a compiler error saying I can&#39;t implicitly convert `bool?` to `bool`.

Why is one different from the other?

Trying to understand ?. (null-conditional) operator in C#

In old .NET we used to be able to run the `csc` compiler to compile a single .cs file or several files.

With .NET Core we have `dotnet build` that insists on having a proper project file. Is there a stand-alone  command line compiler that would allow to compile source code files without having a project (and listing referenced dependencies on the same command line)?

On Linux, when I have the old `csc` and the new .NET Core installed, I get these timings:

    [root@li1742-80 test]# time dotnet build
    Microsoft (R) Build Engine version 15.3.409.57025 for .NET Core
    Copyright (C) Microsoft Corporation. All rights reserved.

      test -&gt; /root/test/bin/Debug/netcoreapp2.0/test.dll

    Build succeeded.
        0 Warning(s)
        0 Error(s)

    Time Elapsed 00:00:03.94

    real    0m7.027s
    user    0m5.714s
    sys     0m0.838s

    [root@li1742-80 test]# time csc Program.cs
    Microsoft (R) Visual C# Compiler version 2.3.0.61801 (3722bb71)
    Copyright (C) Microsoft Corporation. All rights reserved.


    real    0m0.613s
    user    0m0.522s
    sys     0m0.071s
    [root@li1742-80 test]#

Note 7 seconds with .NET Core versus several hundred milliseconds with the old `csc` for the same file, `Program.cs`.

I&#39;d like to be able to compile as fast with .NET Core as I used to be able with `csc`.





Is it possible to compile a single C# code file with the .NET Core Roslyn compiler?

String interpolation in C#6 lets me write:

    decimal m = 42.0m;
    string x = $&quot;The value is {m}&quot;;

However, a very common use case for string formatting is to specify the locale used for formatting the values. Let&#39;s say I need to use `InvariantCulture` for the formatting operation above, what is the syntax for that ? 

[This discussion][1] suggests that I should be able to do this:
    
    string x = INV($&quot;The value is {m}&quot;);

Where INV is defined as

    public static string INV(IFormattable formattable)
    {
        return formattable.ToString(null, System.Globalization.CultureInfo.InvariantCulture);
    }

However, this does not work. It compiles, but it leaves my program hanging at in cmd.exe at startup - as if klr.exe, that I assume is being invoked, hangs (Compiler bug?)

This is an ASP.NET 5 Console Project in VS15 CTP 6.

  [1]: https://roslyn.codeplex.com/discussions/570292

Specifying locale for string interpolation in C#6 (Roslyn CTP6)

For some reason, even so much as typing this into a C# file in Visual Studio is enough to cause it to instantly crash. Why?

    unsafe struct node {
        node*[] child;
    }

It seems to occur when the IDE would start coloring keywords and the like.

Trying it in TIO spits out `csc.exe exited with code 1` which isn&#39;t very helpful.

While array declarations in C# are different than in C/C++, the above &lt;i&gt;seems&lt;/i&gt; like it should be perfectly valid. Why isn&#39;t it, and why does it crash Visual Studio?

My Visual Studio version is 14.0.23107.

Why does this code crash Visual Studio 2015?

I just recently downloaded and installed Visual Studio Professional 2015 (14.0.23107.0). The first time I opened up our solution (28 projects) and performed a Build -&gt; Rebuild Solution, my development machine came to an absolute crawl. The CPU was maxed out at 100% and the build never completed - even after &gt; 10 minutes.

I opened up Windows Task Manager and noticed: &gt; 10 VBCSCompiler.exe tasks running. When combined, these tasks sent the CPU &gt; 90%.

Any idea why there are so many of these tasks running? Any way to stop this from happening?

This is the closest thing I can find to someone else experiencing the same issue: https://github.com/dotnet/roslyn/issues/2790

**Update (8/7)**

-Hans Passant, great thought. My manager provided me with this release (14.0.23107.0). Is this the correct version for the &quot;official release&quot;?? I did not knowingly install any of the per-release versions of Visual Studio 2015. I don&#39;t think there are any beta bits lying around.

-Kyle Trauberman, I&#39;m not that familiar with environment variables in the context of Visual Studio; however, I naively ran `set DisableRosyln=true` in a VS (and MSBuild) Command Prompt Window. This did not seem to have any impact. VBCSCompiler.exe showed right back up even after restarting VS2015.

I repaired my VS2015 install and performed a reboot. This did not help.

**Update Part 2 (8/7)**
-Hans Passant, very impressive write up!! Although, the problem didn&#39;t happen this time around, I took a look at the things you described:

As far as the modules loaded with the VBCSCompiler.exe, here&#39;s what I have:

[![enter image description here][1]][1]

It&#39;s interesting that our .NET core assemblies are at different versions. You&#39;re at 4.06.79 while, I&#39;m at 4.06.81.

My &quot;client side dlls&quot; (located at C:\Program Files (x86)\MSBuild\14.0\Bin\Microsoft.Build.Tasks.CodeAnalysis.dll) are at the same version and time stamp as yours:
[![enter image description here][2]][2]

Oddly enough, when I look at the code in ILSpy, I see something slightly different - optimization perhaps?

        private static NamedPipeClientStream TryAllProcesses(string pipeName, int timeoutMs, CancellationToken cancellationToken, out string newPipeName)
    {
    	string str = pipeName;
    	int num = 1;
    	while (File.Exists(string.Format(&quot;\\\\.\\pipe\\{0}&quot;, pipeName)))
    	{
    		NamedPipeClientStream result;
    		if ((result = BuildClient.TryConnectToProcess(pipeName, timeoutMs, cancellationToken)) != null)
    		{
    			newPipeName = pipeName;
    			return result;
    		}
    		pipeName = str + &quot;.&quot; + num.ToString(CultureInfo.InvariantCulture);
    		num++;
    	}
    	newPipeName = pipeName;
    	return null;
    }

**Let me get back with you on the specific pipname argument passed to the instances of VBCSCompiler.exe. I will have to wait until it happens again.

  [1]: http://i.stack.imgur.com/rPd61.png
  [2]: http://i.stack.imgur.com/kcXmI.png

All Roslyn Solutions on Gang of Coders

Total of 26 Roslyn Solutions

C# 7.3 Enum constraint: Why can't I use the nullable enum?