Question about operations on class/struct properties

[Phil Lavoie via Digitalmars-d-learn]

All you said makes sense. If there is a direct connection between 
getter, setter and member than yes, returning it by reference is 
usually more convenient:

private T _member;
@property ref inout(T) member() inout {return _member;}

However, sometimes, there is no direct connection between field 
and mutators. Sometimes, it is calculated on the fly.

Date {
  ...
  @property auto hour() {return magic / someNumber;}
  @property void hour(int newHour) {//complicated algorithm to set 
the hour.}

}

Now, assuming we have these two mutators, operators could be 
automagically implemented.

Date myDate;
myDate.hour += 4; //myDate.hour(myDate.hour() + 4)