Why can't c# use inline anonymous lambdas or delegates? [duplicate]

Question

I hope I worded the title of my question appropriately.

In c# I can use lambdas (as delegates), or the older delegate syntax to do this:

Func<string> fnHello = () => "hello"; Console.WriteLine(fnHello());  Func<string> fnHello2 = delegate() {     return "hello 2"; }; Console.WriteLine(fnHello2()); 

So why can't I "inline" the lambda or the delegate body, and avoid capturing it in a named variable (making it anonymous)?

// Inline anonymous lambda not allowed Console.WriteLine(     (() => "hello inline lambda")() );  // Inline anonymous delegate not allowed Console.WriteLine(     (delegate() { return "hello inline delegate"; })() ); 

An example that works in javascript (just for comparison) is:

alert(     (function(){ return "hello inline anonymous function from javascript"; })() ); 

Which produces the expected alert box.

UPDATE: It seems you can have an inline anonymous lambda in C#, if you cast appropriately, but the amount of ()'s starts to make it unruly.

// Inline anonymous lambda with appropriate cast IS allowed Console.WriteLine(     ((Func<string>)(() => "hello inline anonymous lambda"))() ); 

Perhaps the compiler can't infer the sig of the anonymous delegate to know which Console.WriteLine() you're trying to call? Does anyone know why this specific cast is required?

Answer 1

Lambdas in C# do not have types, until they are used in a context that casts them to a delegate or Expression type. That's why you can't say

var x = () => "some lambda"; 

You might enjoy

http://blogs.msdn.com/ericlippert/archive/2007/01/11/lambda-expressions-vs-anonymous-methods-part-two.aspx

http://blogs.msdn.com/ericlippert/archive/2007/01/12/lambda-expressions-vs-anonymous-methods-part-three.aspx

Answer 2

It seems to work if you give it a type cast:

String s = ((Func<String>) (() => "hello inline lambda"))(); 

Is it useless? Not entirely. Take the below:

String s; {     Object o = MightBeNull();     s = o == null ? "Default value" : o.ToString(); } 

Now consider this:

String S = ((Func<Object,String>)(o => o == null ? "Default value" : o.ToString())     )(MightBeNull()); 

It's a little ugly, but it is compact.