用=>初始化（这样）

Question

I've been looking into Entity Framework 7 source code on github and I've found following property initialization in TableExpressionBase.cs

public override ExpressionType NodeType => ExpressionType.Extension;

I have never seen such usage of => operator in C#. I've also looked what is new in C# 6.0, however I haven't found this construct. Can someone explain what is the purpose of it?

Thanks.

Answer 1

This is the new expression-bodied members syntax that was added in C# 6.0.

This article has a good rundown of the things that was added, look for the heading "Expression Bodied Functions and Properties" about 3/4 down the article.

In C# 6.0 a lot of syntax was added that generates code under the hood. It doesn't allow you to do stuff that you couldn't do before, but it makes the number of lines of code you have to write smaller.

Specifically, if you have a property like this:

public TYPE Name
{
    get
    {
        return EXPRESSION;
    }
}

Then you can now write this property like this:

public TYPE Name => EXPRESSION;

The compiled code will be identical so you can pick and choose which one of the two syntax variations you want to use.

You can do the same thing with methods:

public string Name(int PARAM1, string PARAM2)
{
    return string.Format("{0}, {1}", PARAM1, PARAM2);
}

can become:

public string Name(int PARAM1, string PARAM2) => string.Format("{0}, {1}", PARAM1, PARAM2);

That's all there is to it.

Specifically, the property you saw in the EF7 code is basically the same as this:

public override ExpressionType NodeType
{
    get
    {
        return ExpressionType.Extension;
    }
}

Answer 2

It's a new C# 6.0 feature as you suspected.

Properties and indexers can have getters and settersgetter-only properties and indexers can have an expression body:

 public string Name => First + " " + Last; public Customer this[long id] => store.LookupCustomer(id); 

http://blogs.msdn.com/b/csharpfaq/archive/2014/11/20/new-features-in-c-6.aspx

Its simply a shorter way to define a getter for a property.