Can't use an "inline" array in C#?

Question

Imagine you have this somewhere

public static T AnyOne<T>(this T[] ra) where T:class     {     int k = ra.Length;     int r = Random.Range(0,k);     return ra[r];     } 

or even just this

public static string OneOf(this string[] strings)     {     return "a";     } 

Then, of course you can do this...

string[] st = {"a","b","c"}; string letter = st.AnyOne(); 

... which is great. BUT. It would appear you can NOT do this:

string letter = {"a","b","c"}.AnyOne(); 

or indeed perhaps this

string letter = ( {"a","b","c"} ).AnyOne(); 

or anything else I tried.

In fact (1) why can one not do that? and (2) am I missing something, how would you do that if there is a way?

Answer 1

You have to create the array first, using new[].

string letter = (new[] {"a","b","c"}).AnyOne(); 

As @hvd mentioned you can do this without parantheses (..), I added the parantheses because I think it's more readable.

string letter = new[] {"a","b","c"}.AnyOne(); 

And you can specify the data type new string[] as on other answers has been mentioned.

---

You can't just do {"a","b","c"}, because you can think of it as a way to populate the array, not to create it.

Another reason will be that the compiler will be confused, won't know what to create, for example, a string[]{ .. } or a List<string>{ .. }.

Using just new[] compiler can know by data type (".."), between {..}, what you want (string). The essential part is [], that means you want an array.

You can't even create an empty array with new[].

string[] array = new []{ }; // Error: No best type found for implicity-typed array 

Answer 2

(1) why can one not do that? {"a","b","c"}.AnyOne();

This line:

string[] st = {"a","b","c"}; 

is a short hand for an equivalent array creation expression (under ILSpy)

string[] st = new string[]  {"a","b","c"}; 

This string[] st = {"a","b","c"} can only be used at the time of declaration, you can't not use it elsewhere, you can't even do:

string[] st; st = {"a", "b", "c"}; //Error 

It is explained under Section 7.6.10.4 for Array Creation expression in C# language specifications.

So this "{"a", "b", "c"}" alone without usage in declaration means nothing. Hence you can't use it with your extension method, as your extension method operates on an array.

(2) am I missing something, how would you do that if there is a way?

Already mentioned in @adricadar's answer, you can do:

(new[] {"a","b","c"}).AnyOne(); 

or

(new string[] {"a","b","c"}).AnyOne();