I've inherited an app. The app has to use .NET 2.0. However, I would like to make use of a feature introduce in C# 4.0 (optional arguments). I understand that a framework is separate from a language. However, what I'm not sure of is, can I use this C# feature in the context of .NET 2.0?
The code compiles. I wasn't sure if this was legitimate, or if I just got lucky :).
Thank you for your insights.
Optional arguments/parameters have been supported in CLR since CLR 1.0. This is due to CLR support for VB.net.
This is why your code compiles. Other new 4.0 features may not work the same.
Other post-C# 2.0 features that will compile into a .NET 2.0 application include named arguments, lambda expressions, auto properties, & extension methods.
Related
I created a project in Visual Studio 2017 RC to check whether I can use new C# 7.0 language features in a .NET Framework 4.5 project. It seems to me that after referencing System.ValueTuple NuGet, new tuples are working fine. Is there anything else I should think about, or is this going to work?
After checking System.ValueTuple NuGet dependencies, it looks like .NET Framework 4.0 is not supported. Is this the case, or is there some way to make the new language work in this runtime also?
Let's go through the features new in C# 7.0:
Tuples: The System.ValueTuple package has a version for the portable-net40+sl4+win8+wp8 profile. That means it is usable on .Net 4.0. (Not sure why dependencies list only .Net 4.5.)
If you wanted to use tuples on even lower versions of .Net, it should still work, as long as you add the code for ValueTuple and related types to your project.
out variables, pattern matching, local functions, more expression-bodied members, throw expressions, numeric literal syntax improvements: All these features are just syntax sugar, so they don't need any new capabilities from the framework.
ref locals and returns: This feature exposes in C# what the framework supported since the start, so no changes in the framework are needed here either.
Generalized async return types: To use this feature, you need a type that has the AsyncMethodBuilder attribute, which is in the System.Threading.Tasks.Extensions package (along with one such type, ValueTask<T>). This package is only supported on .Net 4.5, so for .Net 4.0, you would need to compile the relevant types yourself. (Using await on .Net 4.0 also requires Microsoft.Bcl.Async, but that's nothing new.)
To sum up: All of C# 7.0 should work on .Net 4.5 after installing the required packages and most of it should work on .Net 4.0 too.
Running a C# 7 compiled application on .NET 4.5 should be fine at this moment, but note that running ASP.NET applications that use ASP.NET Dynamic Compilation won't work on .NET 4.5 because the C# 7.0 compiler requires .NET 4.6 to run.
Source: https://github.com/dotnet/roslyn/issues/17908:
The C# 7.0 compiler (2.0 and higher) requires .NET 4.6 to run
The information on https://www.nuget.org/packages/Microsoft.Net.Compilers/2.0.1 (about supporting .NET 4.5) seems to be outdated.
I maintain a .NET 2.0 library (currently, using Visual Studio 2013).
I have used a code-inspection tool on the code of the library and was surprised when the tool suggested using ?? operator or lambdas instead of some of the code.
I was even more surprised when I applied suggested edits and the library was successfully built after that.
Why the library with Target Framework set to .NET Framework 2.0 can be built with newer features of C# in it's code?
Is it safe to use newer C# features when building for older .NET Framework versions? I mean, the users of the library can have .NET Framework 2.0 only and I want them to be able to use the library even if I use lambdas in it's code.
.NET 2.0 and C# 2.0 are 2 different things. In your case you could perfectly fine have a .NET 2.0 library (which is targeting the CLR 2.0) and use the C# 3.0 compiler which supports for example lambda expressions.
So you should make a difference between your compiler version and the version of the CLR you are targeting. Since you are using VS 2013, you could use newer versions of the compiler.
Is it safe to use newer C# features when building for older .NET Framework versions?
Yes, perfectly safe. The generated assembly is still targeting the CLR 2.0 and will run without any issues with this older version of the CLR.
Basically, new C# language features can be implemented in the compiler without requiring extensions to the underlying .net framework. It isn't always done like that, but it may be.
In the case of lambdas, they were introduced in C# 3.0. So you need a compiler of that level or above. However, the new features introduced in C# 3.0 were all built using the features of .net 2.0. So you can use lambdas under .net 2.0.
In essence, the new functionality here is implemented in the compiler rather than the framework.
As for the null-coalescing operator, ??, it was introduced in C# 2.0 so there's nothing surprising about being able to use it under .net 2.0.
This is, probably, a very simple answer for someone. I have a method with an Optional Parameter like so;
public static Email From(string emailAddress, string name = "")
{
var email = new Email();
email.Message.From = new MailAddress(emailAddress, name);
return email;
}
Now, I must target .Net 3.5 and it was my understanding that Optional Parameters are part of .Net 4. However, my project builds and I double checked the Properties - Application page which states 3.5 as the target framework. Then I found a article on MSDN saying it's a feature of C#4 in VS2010. (MSDN Article --> Named and Optional Arguments)
Can someone help clarify this for me. C#4 does not require .Net4? What are Optional Parameters ACTUALLY a part of?
Thank you.
Optional parameters have been supported in the CLR since 1.0. Languages like VB.Net's have been using them since the start. While the first version of C# to support them is 4.0, it can still generate valid code for a 2.0 CLR and in fact does so. Hence you can use default parameters in 2010 if you are targeting the 3.5 CLR (or 2.0, 3.0, etc ...)
This type of support is not limited to default parameters. Many new C# features can be used on older version of the framework because they do not rely on CLR changes. Here are a few more which are supported on CLR versions 2.0 and above
Named Arguments: Added C# 4.0
Lambda Expressions: Added C# 3.0
Auto Properties: Added C# 3.0
Extension Methods: Added C# 3.0
Co/Contra Variance: Added C# 4.0
If you compile that up and examine the output using a tool like ILDASM you'll see that the optional parameter is simply implemented by adding an attribute to the metadata that describes the method's formal parameters. As long as that attribute class is available on the target platform there should be no problem with using the emitted code on a downlevel platform.
The language version is independent of the framework version. For C# they happen to run mostly in parallel, i.e. C# 4 and framework 4.0 came with Visual Studio 2010. (However there is no 3.5 version of C#.)
With VB the version numbers are different, as VB 7 was the first VB.NET version. So, VB 10 comes at the same time as framework 4.0.
The optional parameters is a language feature introduced in C# 4. When you use VS 2010 you use C# 4, even if you target framework 2.0, so you can use all C# 4 features.
C# 4.0 is included with Visual Studio 2010, and the C# compiler understands optional parameters. So yes, the C# 4.0 language definition is something different than .NET 4.0. I guess a method with optional parameters compiled for .NET 3.5 will show overloaded methods when opening with eg. VS 2008
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)?
Why I can use Object Initializers in Visual Studio 2008 Windows projects, etc targeted to .NET 2.0 but cannot - in ASP.NET projects targeted to .NET 2.0 ?
I understand that this is C# 3.0 features, but don't - why this possible to use in .NET 2.0 projects.
Probably because the ASP.Net stuff targeting the 2.0 framework assumes it will run in a mode where it may have to compile some code on the fly. Since it is running in 2.0 mode it will get the 2.0 compiler at that stage (thus anything relying on the 3.0 compiler will fail)
When targeting the 2.0 codebase from a 'normal' project the compilation is done then and there so relying on 3.0 compiler functionality is fine.
When you target the .NET 2.0 runtime, you are also targeting the C# 2.0 compiler. That version of the compiler does not understand the 3.0 features.
Here's an existing question that deals with using C# 3.0 features in .NET 2.0 projects. It explains which C# 3.0 features are available, which aren't and how to use them.
In order to help you with any specific difficulty, we'll need specific details.
The best source of information on advanced featured in C# and how they have evolved from C# 1.0 through 3.0 is Jon Skeet's book. He is here on SO quite often and may even offer some additional insight. However, you really should have the book.
A normal ASP.NET Website compiles on the fly, which means it will use the compiler available to that virtual directory on your web server. If it's set to ASP.NET 2.0, it will use the 2.0 compiler (not the 3.0 compiler targeted to .NET 2.0).
I assume when you convert your website to a web application you WILL be able to target 3.0 and still use some of the 3.0 features. I suggest trying that, I would, but I don't have the time at the moment. Let us know if it works ;-)