When you assign a value to a variable that still has an unknown type, its type will be inferred as being the one of the assigned value, so for example, if you write:

var s;s = "Hello World";

The type of s will be inferred to String.

In addition, if you assign the value of a variable that still has an unknown type to a variable that is of a known type, the type will also be inferred:

      var s;
      var t : String;
      t = s;

Here, the type of s is inferred to String.

When you pass a variable to a function, its type is inferred as being the one expected by the function. For example, consider...