This note highlights problems of accessing bare object properties and why accessors are a way to mitigate these problems and also offer additional advantages.

Table of Contents

• Remove acquisition problems which occur when accessing bare properties
• Prevent code duplication
• Offer casting and default values
• Related Articles

Remove acquisition problems which occur when accessing bare properties¶

Short example using given a and b objects.

  a.title = 'foo'
  # This is not set because the user has not input any value,
  # still it's defined as an acceptable property for object b
  # in its property sheet.
  #b.title = ''
  wrapped_b = b.__of__(a)
  wrapped_b.title # Evaluates to 'foo'

Here, getting the value of the title property on wrapped_b will produce a different result if the user put a value in it or not: in once case it will be the value as set on the document itself, in the other case it will be the value as set on one of it's parents in the acquisition chain. But as accessors are defined on objects' class, the property value won't be acquired from a parent if it's declared as a property of the object itself:

  wrapped_b.getTitle() # Evaluates to the default value defined in the property sheet

Now the result is consistent whether or not the property is set "physically" on the object or not, without removing the advantages of acquisition.

Prevent code duplication¶

Offer casting and default values¶

Related Articles¶