I created new project in Visual Studio with target framework 2.0. But even if I left somewhere var keyword Visual Studio successfully compiles project. Is this the correct behavior as var is 3.0 feature? Is there any settings to prevent code with var to be compiled?
var is a feature of C# 3.0, but it doesn't require any framework features. In other words, it's absolutely fine to use within a project targeting .NET 2.0. The same is true of many other features - anonymous types, automatic properties, lambda expressions etc.
See my versions article for more information. (I need to update it for C# 4 at some point...)
If you want to restrict yourself to C# 2.0, you can specify the language version by clicking on "Advanced" in the Build tab of the project properties, IIRC. (It's definitely there somewhere, but I'd rather have a cup of coffee than check for the exact location right now.)
var is purely a compile-time feature, once the assembly is compiled, the compiler inserts the actual type and the fact that you had used var is "lost".
So a project that's targetting version 2.0 of the framework can still make use of the var feature, because it doesn't actually affect the outputted assembly in any way.
As long as your project will always be compiled with Visual Studio 2008 or newer, you're safe to use C# 3.0 features. The .NET 2.0 target only restricts what libraries you can use, not what language features.
Either do full text replace of var by 1var1 and manually replace them or use pre 3.0 versions of compiler.
Related
I have a legacy application that uses .NET 4.
I tried to use a C# 6 feature when I was changing the code, but my visual studio generates the following error:
Feature 'interpolated strings' is not available in C# 4. Please use language version 6 or greater.
I was wondering if there is a way to use the features of the latest versions of C# without updating the version of the framework?
Or is the C# version directly linked with the framework?
obs: updating the framework is not an option.
The language-version only relies on the version of Visual Studio. To use features intorduced in C#6 you need at least VS2015. This has nothing to do with the installed .NET-framework-version. In fact you can use VS2015 and its compiler-features (e.g. auto-implemented properties with an initial value) and compile against .Net 2.0:
int MyProperty { get; set; } = -1;
To change the target-framework (e.g. .Net 2.0) use Project properties-->Application-->Target framework.
To change the language version via Project properties-->Build-->Advanced-->Language version.
Let´s consider the following example: Beginning with C#3 you can write the following:
var a = new { MyProperty = 1 };
This compiles for any .Net-version. However the most common use-case for anonymous types is when using Linq to fetch data from a database. Linq was introuced in framework-version 3.5 and heavily depends on lambda-expressions and extension-methods, which both were introduced in C#3:
var result = myCollection.Select(x => new { MyProperty = x.MyProperty });
So although you could use anonymous types in earlier versions of the framework, there was little need to do so.
To get a better view on the difference between the C#- (=language)-version and the framework-version read this post. This thread on the other side lists the language-versions and in which version of VS they were released.
The Language version is a Compiler feature, not a runtime one.
Regardless which source code language language or source code language version you use, the end result will always be the same MSIL code. You can freely pick which Framework version to compile against. Which limits your available .NET Libraries. But it does not affect the C# version you are using in any way.
Of course there might be some Language Features that make little sense without supporting libraries. I can just not think of a concrete example of the top of my head.
Edit: Remembered a concrete example: Named and Optional Parameters. IL always supported that. VB.Net had that already for ages. It was a very important part of COM compatibility, especially using the Office COM inter-op. But Prior to C# 4 we C# programmers could not use it: https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/named-and-optional-arguments
You Need Either Visual Studio 2013 or # 2015 to use c sharp version 6 u can change the .net version in the project settings. .NET version Wont be a problem
The build machine where I work still uses the .Net 2.0 compiler.
I've set up Visual Studio to target the .Net Framework 2.0, but when I use the keyword var, it's compiling (since the compiler automagically change the type). But it breaks on the build machine compiler.
Is there a way to setup Visual Studio to break on those things, or even force it to use the 2.0 compiler, so that I won't make the mistake to break the build by using "too new" functionalities?
If I remember correctly, each version of .Net was tied to a specific version of DevStudio and it isn't possible to change this. If you need to compile for .Net 2 then you need the VS2005 compiler. One way to solve this is to use makefiles rather than the IDE to build the application and specify explicitly which compiler is used for each file.
What can be the issues if I build a solution where all the projets are under targetFrameworkVersion=2.0 but one with targetFrameworkVersion=3.5 and
None of the 3.5 features are used
Some of the 3.5 features are used but the classes calling the 3.5 code are never instanciated
Some of the 3.5 features are used in some classes, the classes are instanciated but the code in 3.5 never called
the 3.5 code is called
It depends on what you mean by "features". There are compile-time features like the var keyword and lambda expressions and there are run-time features like LINQ or WCF that require libraries in the .NET 3.x runtime.
I assume you're using Visual Studio 2008, which will handle all the compile-time features. If all you're using is the compile-time features, then everything will work fine in all cases. I do this rather often on my current project.
If you're using run-time features then I believe this is how it will shake out:
Things will just work.
I think this will just work also.
It depends on when static functions are JITted and if you have any 3.5 library referencing code in static functions.
Probably MissingMethodException when a function containing a 3.5 library feature is called.
Rather than worry about all of this, if you're planning on using run-time features, I would simply add a key to the App.config that the 3.5 runtime is required and it'll check on startup and bomb if it isn't present. Then you don't need to figure out all these permutations and your application will be more stable.
First of all, you need to be aware that what you are targeting is actually .NET 2.0 SP1.
How are your projects related? Do you have projects that are built under .NET 2.0 which reference the .NET 3.5 project (or vice versa)?
I am coding in VS2008 with Resharper 4.5.1, but the projects are set to target .NET Framework 2.0.
Still, Resharper is making suggestions that are relevant to the .NET 3.5 framework. For instance, it tells me that I should be using collection initializers, etc...
I've looked through the settings and can't seem to find the checkbox to tell it to give 2.0 specific advice.
Select your project in the Solution Explorer and open the Properties tool window (F4 in the standard keyboard layout or View > Properties Window after selecting the project). In the ReSharper section, there is a Language Level property that you can set to C# 2.0. Note that there are two separate project properties windows that manage different properties, if you see tabs for "Application", "Build" and "Debug" you are in the wrong window.
As others have said, this affects the version of C#, not the version of the framework (since most of the C# 3.0 changes can be compiled to an assembly that targets .NET 2.0).
Those features are not .NET 3.5 framework features, but merely features of the 3.5 compiler. And since in VS2008 this is the compiler invoked for .NET 2 targets, it does handle these syntax extensions correctly.
I'm looking to write a library that uses the new optional parameters feature of C# 4.0, but I want to target it to the 3.5 version of the framework. Is this possible?
Are optional parameters syntactic sugar in the same way that extension methods are?
With VS2010 RC, I was able to create a .NET 3.5 application that uses optional parameters in C#.
So yes, it's all about syntactic sugar.
VS 2010 supports optional parameters in C# for .NET 3.5 solutions. One caveat however, is that the command-line compiler will report errors.
So, if you have automated builds in running, - using NANT or something else using the command-line compiler - your builds will fail.
Like Jon Skeet I was getting "Feature 'optional parameter' cannot be used because it is not part of the 3.0 C# language specification". However in the RTM version of Visual Studio you can select Language Version to "default" in Project Properties->Build->Advanced. That got it to work for me.
You can use optional and named parameters in a targeted framework of a previous version as long the assemblies are build within a development environment for v4 (f.e. VS2010). But you should be aware of runtime compiling or publishing websites in this case the compiler of the targeted framework will be used. And because the compilers of the older frameworks doesn't understand the syntax of optional and named params it will results in compiler errors.
Go to project properties -> Build Tab -> click button 'Advanced' -> set language version to 'default' -> save -> be happy ;)
I don't have VS2010 installed here to check, but I believe this would be purely a language feature, and therefore should be usable regardless of the framework being targeted.
Edit: Looking at this link (and a few others), it appears that optional parameters compile to method arguments with an [opt] attribute in the il. I don't know if this parameter existed in previous versions of the clr, but still my guess would be that it does.
VB.NET has optional parameters if you want to use optional parameters in .NET 3.5.