Generic methods <string> vs <T,U>

Question

I didn't understand the explanation in the lesson

If you have a single type parameter you need to explicitly name it ?

string x = "Hello";
string y = "World";
Swap<string>(ref x, ref y);//<----- <string>
//Now x is "World", y is "Hello"

If you have 2 different type of parameters do not need to name the type explicitly.
static void Func<T, U>(T x, U y) {
Console.WriteLine(x+" "+y);
}
static void Main(string[] args) {
double x = 7.42;
string y = "test";
Func(x, y); //<---- I would expect something like Func<string, double>(x,y);
}

Why is it that if you have a single parameter in a generic method you need to name the type like Swap<string>(ref a, ref b) and if you have more parameters you do not need it like Func(x,y)

It does work though
https://code.sololearn.com/cwlo7qP7T8rR

Answer 1

You can even leave the <string> away. When the compiler processes your code, he knows what types your variables have (you initialize the variables with their type declared in the beginning). The <> is optional, but not necessary.

Answer 2

Thank you for your explanation. It works.