C# double lambda (currying)

Question

C++ / C#

Please explain this expression:

class Program
    {
        static Func<string, Func<string, string>> func;
        static void Main(string[] args)
        {
            func = a => b => a = b;
        }
    }

Answer 1

Here is an example of usage.

static Func<T1, Func<T2, Func<T3, TResult>>> Curry<T1, T2, T3, TResult> 
    (Func<T1, T2, T3, TResult> function) 
{ 
    return a => b => c => function(a, b, c); 
}

Alas, I did not succeed in trying to formulate an explanation better than the article. In fact, you can call a function that will return a function, one of whose parameters will be the parameter passed to the first function .... In general, a function of two arguments yields 2 functions of 1 argument, but the second function is a derivative of the first.
In your example, there is not much logic, but the call can be like this:
In this case, the value of the first parameter will be assigned to the second, but are strings, nothing will happen to the first one.

Answer 2

Thanks @Vadimyan . Indeed, such constructions are used when currying a function. Initially, I simply could not understand the construction like func (a) (b) and could not even find in Google what this expression means. But now everything has become on the metsa.