Smalltalk and Object Orientation: an Introduction - Free

This is a very powerful class which greatly simplifies the production of ordered lists of information.
You can change the block controlling the sort by sending the message sortBlock: to the
sortedCollection instance with a new block definition.
11.3 List
The List class is a recent addition to the collection classes in VisualWorks (which is not yet available
in other implementations of Smalltalk such as Visual Smalltalk). The List class combines some of the
more useful features of the Array, OrderedCollection, SortedCollection classes and the
Model class. The order of its elements is initially determined by the order in which the elements are
added (as in OrderedCollection). These elements can then be accessed via an index (as in
Array). However, the elements can also be sorted using either the default ascending order, or a custom
sort block can be provided (as in SortedCollection). In addition a List keeps a record of
dependents to which it should send updates (as in class Model). However, as we have not yet looked at
the Model class, we will ignore this part of the class’s operation.
The set of features provided by this class make it one of the most widely used types of collection, in
some cases supplanting the older OrderedCollection and SortedCollection classes. It responds to a
combination of the Ordered and Sorted Collection class protocols. Therefore it understands after:,
before:, sort, sortWith:, add:, add:after: and add:before:. It also responds to
addLast:, addFirst:, remove:ifAbsent:, removeFirst, removeLast etc.
To create a new instance of class List use either new or new: depending on whether you wish to
specify an initial size or not.
For example, try this out in a Workspace.
| temp |
temp := List new: 10.
temp add: 'John'.
temp addFirst:'Paul'.
temp add: 'Peter' before: 'John'.
temp inspect.
11.4 Intervals
Instances of class Interval represent finite arithmetic progressions. Such progressions are given by a
starting number, a (finite) limit, and a method of computing the next number. Once created, new
elements cannot be added or removed from the Interval.
Intervals can be created using the class messages:
from: start to: stop
from: start to: stop by: step
start, stop and step can be any kind of Number. Intervals are common enough that a shorthand
form has been provided. This shorthand form is achieved by sending to: or to:by: to a kind of
Number. For example the following are equivalent:
Interval from: 10 to: 100 by: 2
10 to: 100 by: 2
These are equivalent to a for i = 10 to 100 step 2 type loop. However, they actually create
an interval containing all the obje cts to be processed before any further processing occurs. This
allows them to be used with a do loop.
Intervals respond to the message do: aBlock by evaluating aBlock for each of its values
in sequence. Thus, an Interval can be used to construct the equivalent of a FOR loop. For example:
(10 to: 100 by: 2) do: [:each | Transcript show: each printString].
This is therefore roughly equivalent to the C for loop:
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