Multiple implicit type converters

[Bahman Movaqar via Digitalmars-d-learn]

As only one `alias this` is possible for any type, how should one 
implement multiple implicit type converters?

Actually I'm looking for something similar to Groovy's `asType` 
method[1].  An example in Groovy:

    Point p = new Point(1, 1)
    assert (p as BigDecimal[]) == [1, 1]
    assert (p as BigDecimal) == Math.sqrt(2)
    assert (p as Region) == new Region(p, p)

This allows for multiple type converters which are *explicit* 
--in contrast to `alias this` implicit nature.

[1] 
http://docs.groovy-lang.org/latest/html/groovy-jdk/java/util/Collection.html#asType%28java.lang.Class%29