December 21, 2024
The Protocol of OrderedCollection
This is an illustration of OrderedCollection instance topEarners.
| 1 | 2 | 3 | 4 | 5 | 6 |
|---|---|---|---|---|---|
| 'Bill Crynge' | 'Sian O''Driscoll' | 'Bryan Walker' | 'Herve Constantine' | 'Phillipa Reynolds' | 'Terry Cook' |
However, the following year, another artist, Mark Wolfe, exhibiting for the first time in three years, pulls out all the stops and secures number one spot. The gallery is forced to revise topEarners
topEarners addFirst: 'Mark Wolfe' which returns
the argument and the revised collection is now textually represented as
OrderedCollection ('Mark Wolfe' 'Bill Crynge' 'Sian O''Driscoll' 'Bryan
Walker' 'Herve Constantine' 'Phillipa Reynolds' 'Terry Cook')
Cordelia's reservations about Bill Crynge are partially justified
by the final cost of rebuilding the gallery after his last show. Crynge
barely makes the cut, but still holds on to his place in topEarners.
How can the collection be revised?
topEarners addLast: 'Bill Crynge' will place
Bill at the end of the line, but the result will be two occurences of
the string'Bill Crynge', proving that you
can have duplicates in an ordered collection. The following code will
put Bill in his rightful place and avoid this problem
topEarners remove: 'Bill Crynge';
add:
'Bill Crynge' after: 'Terry Cook'
The message answer is 'Bill Crynge'
topEarners is now textually represented as
OrderedCollection ('Mark Wolfe' 'Sian O''Driscoll' 'Bryan Walker' 'Herve
Constantine' 'Phillipa Reynolds' 'Terry Cook' 'Bill Crynge')
Care has to be taken when using remove:
it is safer to use remove:ifAbsent:
Further revision is needed as one more artist has turned paint into gold. In with a bullet at number five is RCA graduate Will James. There are several ways of adding him to Cordelia's chosen few.
topEarners add: 'Will James' before: 'Phillipa Reynolds' answering
with 'Will James'
or
topEarners add: 'Will James' beforeIndex: 5 answers with the updated
collection, the representation of which is
OrderedCollection ('Mark Wolfe' 'Sian O''Driscoll' 'Bryan Walker' 'Herve
Constantine' 'Will James' 'Phillipa Reynolds' 'Terry Cook' 'Bill Crynge')
If you know the index of an element that you wish to update then
at:put: can be used as in
topEarners at: 8 put: 'Claudia Beckmann' answering
with 'Claudia Beckmann' the collection is
now textually represented as
OrderedCollection ('Mark Wolfe' 'Sian O''Driscoll' 'Bryan Walker' 'Herve
Constantine' 'Will James' 'Phillipa Reynolds' 'Terry Cook' 'Claudia Beckmann')
topEarners at: 1 answers with 'Mark Wolfe' as does
topEarners first
topEarners last answers with 'Claudia Beckmann'
Messages such as size, isEmpty, includes: are all implemented as expected
The gallery has another collection in its system and records the type of work it sells. The added string elements are 'Painting', 'Print', 'Drawing', 'Sculpture' and 'Installation'.
salesTypeCollection := OrderedCollection new.
After each sale the collection grows with the addition
of messages like
salesTypeCollection add: 'Painting' and
so on. At any stage the number of sales of any kind of work can be counted
by a looping do: message. Again we
need to initialise a temporary variable count to zero, then loop through
the collection, testing each element in turn for equality with the element
that we are searching for. For example
|count|
count := 0.
salesTypeCollection do: [:element| (element = 'Painting')
ifTrue:
[count := count + 1]].
^count
So far, all these elements have been strings, but they could be any object.
Now consider a different scenario.
Next page » The exhibition collection
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