问题
I have a project that targets older versions of the .NET framework (.NET 4.5.2). I installed Visual Studio 2015 (and therefore .NET 4.6 on my machine). I noticed that if I use C# language features released in .NET 4.6/C# 6, it still compiles. If my project's target framework is < .NET 4.6, shouldn't this not compile:
public string MyExpressionBodyProperty => "1";
//auto properties are new in C# 6
public string MyAutoProperty { get; } = "1";
private static void MethodThatUsesNameOf(string filename)
{
if (filename == null)
{
//nameof was released in C# 6
throw new ArgumentException("The file does not exist.", nameof(filename));
}
}
How can I ensure I'm only using .NET language features that work with the framework version I'm targeting?
回答1:
The .NET Framework version and the C# language version are different things. The C# 6 language features
public string MyAutoProperty { get; } = "1";
nameof(filename)
can be compiled by VS 2015 into code that targets earlier frameworks.
How can I ensure I'm only using .NET language features that work with the framework version I'm targeting?
If you try to use a .NET 4.6 Framework feature, you will get an appropriate compiler error if you are targeting an earlier framework.
Would I be able to deploy this code to machine which did not have .NET 4.6?
Yes, you would. As long as the deployment machine has a framework compatible with the one you target in VS2015.
回答2:
There are C# 6 features and .NET 4.6 features.
nameof is a C# 6 feature so only needs to be running on a newer compiler but can still use the older .NET framework.
An example of a feature that requires .NET 4.6 is the following:
public void Foo(IReadOnlyCollection<string> input)
{
}
public void Main(string[] args)
{
Foo(new Stack<string>());
}
In .NET 4.6 Stack implements IReadOnlyCollection but in previous versions it does not. The above code would fail to compile if you selected .NET 4.5.2 as your target platform.
来源：https://stackoverflow.com/questions/31570654/why-does-net-4-6-specific-code-compile-when-targeting-older-versions-of-the-fra