HowTo: Use latest C# features in MVC5 Razor views (.cshtml)

Having recently updated an ASP.net MVC web app from MVC4 to MVC5 and from .NET 4.5 to .NET 4.7.2 I was expecting Razor views (.cshtml files) to use the latest C# compiler, especially since at Properties/Build/Advanced option for the web project one read “C# latest major version (default)”.

However that was not the case and trying to use newer C# language features like the ?. ternary conditional operator or interpolated strings (or nameof etc.) would show errors like

Feature ‘interpolated strings’ is not available in C# 5. Please use language version 6 or greater.

Luckily there is a workaround for using the latest C# compiler in MVC5. Just need to add the NuGet package https://www.nuget.org/packages/Microsoft.CodeDom.Providers.DotNetCompilerPlatform/ to one’s project as explained at https://dusted.codes/using-csharp-6-features-in-aspdotnet-mvc-5-razor-views. Alternatively one could move their project to ASP.net Core, which is a more drastic move though.

After doing it I started seeing Intellisense issues in .cshtml like:

The type ‘Expression<>’ is defined in an assembly that is not referenced. You must add a reference to assembly ‘System.Core …

Tried to add the System.Core assembly to the project, but wasn’t allowed (it said the Build system was adding it). Adding System.Core as a NuGet package would mean moving to .NET Core which I wasn’t ready to try with that project yet.

Seems there was an easy solution to that, just closed and reopened the Visual Studio solution and did a Rebuild and all was fine after that.

HowTo: Make Project Linker extension’s VSIX install at Visual Studio 2012

Project Linker is a Visual Studio Extension that “helps to automatically create and maintain links from a source project to a target project to share code that is common to Silverlight and WPF”.

In ClipFlair, where I have shared code between a Silverlight and a WPF project (I guess same would be for XNA projects for Xbox360 and for PC), a practice I use is to put shared files in a “Source” project and add them to both projects as links (using “Open as link” action available from Add file dialog if you press the dropdown arrow next to the “Open” button).

An alternative is to put such files in say the WPF project and use the Project Linker tool from Microsoft Patterns & Practices group to link to those files from the Silverlight project easily.

However, that tool seems to be only available for Visual Studio 2010, not for the newer 2012 version. Luckily, some users have posted a workarround at the discussion there (Reviews and Q&A tabs):

1. Download the .vsix
2. Extract contents with 7-Zip (since .vsix is a .zip file which you can see by renaming to .zip or .vsix.zip)
3. Modify file with extension .vsixmanifest to add <visualstudio version="11.0"> to the <supportedproducts> node
4. Change MaxVersion to <supportedframeworkruntimeedition minversion="3.5" maxversion="4.5" /> (this may not be necessary)
5. Zip up contents again
6. Rename extension back to .vsix
7. Install extension

According to comments there, this works but not for all project types. It works if one links the Silverlight project to the WPF one, but not the other way around. It throws a NullReferenceException somewhere in the extension.

VB gotcha: when If function isn’t equivalent to an If-Then-Else block

Just got bitten by the following:

Dim takeN As Integer = If(Integer.TryParse(EdTake.Text, takeN), takeN, itemsCount)

I had used that instead of writing in 2 lines:

Dim takeN As Integer

If not Integer.TryParse(EdTake.Text, takeN) then takeN = itemsCount

However, there’s an important difference:

“If” is a function, so its arguments are evaluated at call-time. The “If” signature is:

I guess the default is to pass arguments ByVal (by value) and not ByRef (by reference), although I’d expect the signature to specify it explicitly to avoid confusion. When one passes a literal value (say 15) to TruePart or FalsePart it just gets “boxed” into an Object, whereas if one passes an expression (e.g. “takeN+1” or even just “takeN”) it gets evaluated first, then result is boxed and passed as an Object.

So, whereas one might think (esp. if coming from the ALGOL “Call-By-Name” era) the 1st line to be equivalent to:

Dim takeN As Integer

If Integer.TryParse(EdTake.Text, takeN) then takeN = [RESULT OF TRYPARSE] else takeN = itemsCount

in fact it’s equivalent to:

Dim takeN As Integer

If Integer.TryParse(EdTake.Text, takeN) then takeN = [ANY] else takeN = itemsCount

where ANY is whatever the takeN variable one had defined contains.

I thought the VB compiler was warning when using a variable before having assigned a value to it, but it seems in this case it misses to issue a warning. In fact I just tried:

Public ReadOnly Property Take As Integer
   Get
     Dim takeN As Integer
     Return takeN
   End Get

End Property

and it still doesn’t complain. Strange, probably it sets new local variables to 0 by default, but it shouldn’t encourage a programming style that relies on implicit default values – such syntax usually means there’s a mistake in the source code that can lead to a nasty bug.

The moral of the story? Avoid such shorthand expressions and stick to classic keyword-based syntactical structures – after all structured programming had been introduced as an alternative to the many times incomprehensible programs written in functional programming languages (e.g. due to overuse of nested function calls).