By combining extension functions and custom accessors, we get extension properties.
Here, we are adding a
something extension property to a
Map<String, T> for a
declared generic type
can then reference
something on such a
Map, as if
something were implemented
The syntax is reminiscent of extension functions, in that we use
to scope the extension property to the designated class. And, we have to use a
custom getter to define the implementation of how to obtain the value of this property.