Getter With Side Effect

I create a class whose objects are initialized with a bunch of XML code. The class has the ability to extract various parameters out of that XML and to cache them inside the object

Solution 1:

This design pattern is called Lazy initialization and it has legitimate use.

Solution 2:

While the getter certainly performs a side-effect, that's not traditionally what one would consider a bad side-effect. Since the getter always returns the same thing (barring any intervening changes in state), it has no user-visible side-effects. This is a typical use for properties, so there's nothing to be concerned about.

Solution 3:

Quite some years later but well: while lazy initialization is fine in itself, I would definitly not postpone xml parsing etc until someone accesses the object's title. Computed attributes are supposed to behave like plain attributes, and a plain attribute access will never raise (assuming the attribute exists of course).

FWIW I had a very similar case in some project I took over, with xml parsing errors happening at the most unexpected places, due to the previous developper using properties the very same way as in the OP example, and had to fix it by putting the parsing and validation part at instanciation time.

So, use properties for lazy initialization only if and when you know the first access will never ever raise. Actually, never use a property for anything that might raise (at least when getting - setting is a different situation). Else, dont use a property, make the getter an explicit method and clearly document it might raise this or that.

NB : using a property to cache something is not the problem here, this by itself is fine.