C# Inline lambda evaluation

Question

At various times while programming in C# I've found myself in situations where I'd like to define a lambda (or anonymous delegate) and call it in the same line. At this point, the 'cleanest' way I've been able to do this is like this:

bool foo_equals_bar = new Func<String, bool>(str => str.Equals("foo"))("bar");

I would love to be able to do write something like the following instead:

bool foo_equals_bar = (str => str.Equals("foo"))("bar");

Unfortunately, this doesn't seem to work. I would love to know:

1. Is there a simpler way of writing the line of code above?
2. What is returned from (str => str.Equals("foo")) such that is can be used to initialize a Func<String, bool>, but can not be evaluated like a Func<String, bool>?

I should point out that I'm working in C# 3 (VS2008), so if a solution only exists in C# 4, please mention that. (I'd still like to know, even if the solution isn't available to me at the moment).

Thanks

Answer 1

You would need a set of helper methods to make compiler infer lambda types, e.g.:

public static class Functional
{
    public static Func<TResult> Lambda<TResult>(Func<TResult> func)
    {
        return func;
    }

    public static Func<T, TResult> Lambda<T, TResult>(Func<T, TResult> func)
    {
        return func;
    }

    public static Func<T1, T2, TResult> Lambda<T1, T2, TResult>(Func<T1, T2, TResult> func)
    {
        return func;
    }
}

Now you can write:

bool foo_equals_bar = Functional.Lambda(str => str.Equals("foo"))("bar");

Answer 2

str => str == "A" 

is the same as

delegate (string str) { return str == "A";};

So no, there's no way to get just the lambda, since the compiler wouldn't know what type str is if you just said

bool result = (str => str == "A")("B");

EDIT:

Yes, you can add types to lambda expressions, like (string str) => str == "A"; but still, they can't be implicit for some reason. Not sure why. Thanks for the comment, Yuriy.