Question

Since Javascript is the language that I am the most proficient at, I am familiar with using functions as first-class objects. I had thought that C# lacked this feature, but then I heard about Func and Action and delegate, which I think are pretty awesomesauce.

For example, you can declare a Func that concatenates two strings and puts a space between them like this:

Func<string, string, string> concat = (a,b) => a + " " + b;

I noticed that when you type

Func<

the IntelliSense shows that it has 17 overloads:

delegate System.Func<out TResult>
delegate System.Func<in T, out TResult>
delegate System.Func<in T1, in T2, out TResult>
...snip...
delegate System.Func<in T1, in T2, in T3, in T4, in T5, in T6, in T7, in T8, in T9, in T10, in T11, in T12, in T13, in T14, in T15, in T16, out TResult>

That made me laugh. I looked at the MSDN docs for Func and laughed again. This made me try to declare a Func with 17 arguments. It causes an error (Using the generic type 'System.Func<TResult>' requires 1 type arguments).

I can agree that it’s probably not a good idea to have a Func that accepts more than 16 arguments. Even so, this seems like a kludgy way for Func to be implemented. It requires 17 trivially different overloads to be documented. This is all it really should need to know: the last type parameter is the return type, and all the type parameters before it are the argument types.

So what could I do if I wanted to create a Func with more than 16 parameters? Why is there a limit anyway? Why can’t C# just let you declare a Func with an arbitrary number of arguments?

Answer 1

You’re hoping for something like variadic type arguments which C# lacks. C# requires the arity of generic types to be fixed, therefore the heinous proliferation of Func, Action, and Tuple types.

If you’re language shopping, this feature was added in C++11, but you should probably just use jQuery. 🙂