4.2. Motivation

So why should we use accessors instead of doing a direct $person->{'age'} access to the object's property? There are several reasons for that:

1. Writing the property names directly each time is prone to mis-spellings and errors, because they are strings. On the other hand, with method calls, the existence of a particular one is validated at run-time, and will throw an exception if a method was misspelled into a name that is not present.

2. If a property needs to be converted from a first-order property to a calculated value, then one can still use the existing method-based interface to access it, just by changing the implementation of the methods. On the other, this is much more difficult to change with a direct-field access.

3. The external interface provided by methods is cleaner and easier to maintain compatibility with, than a direct class access.

4. There may be other reasons, like better concurrency, persistence, etc.