Why are there Properties in D?

[Marc Schütz" <schuetzm at gmx.net>]

It's true that it hides what happens behind the scenes, but there 
are several advantages. Rikki Cattermole already mentioned 
instrumentation; more generally, this makes it easy to change 
between getter/setter and member variable without modifying all 
the use sites.

I'd like to add generic code. For an example, look at ranges: 
their `front` and `empty` must be callable without parens. This 
makes it possible for some ranges to have a normal member 
variable `front`, or a static enum member `empty` (which can even 
be tested for at compile time!), and for others to use 
methods/UFCS functions instead. Without these, a lot of the 
generic algorithms in `std.algorithm` would be full of 
`is(typeof(range.empty)) || is(typeof(range.empty()))`, or 
similar tests, making them harder to read and get right.