December 21, 2024
The Protocol of Array
By referencing an array with a variable, say baconArray, and evaluating the following expression, an array of sufficient size to store 5 objects is instantiated.
baconArray := Array new: 5
The array's size can be confirmed with
baconArray size
This returns 5
At this stage all the stored elements reference nil.
| 1 | 2 | 3 | 4 | 5 |
|---|---|---|---|---|
| nil | nil | nil | nil | nil |
The next expressions add elements to the array.
fbaconDictionary has already been created, setOfPubs
and birthDate are instantiated as follows:
setOfPubs := Set new.
setOfPubs add: 'French House';
add: 'Colony
Room';
add: 'Dog and
Duck'.
birthDate := Date newDay: 28 month: #October year: 1909.
baconArray at: 1 put: 'Francis Bacon';
at: 2
put: fbaconDictionary;
at: 3
put: setOfPubs;
at: 4
put: birthDate;
at: 5
put: 666
| 1 | 2 | 3 | 4 | 5 |
|---|---|---|---|---|
| 'Francis Bacon' | fbaconDictionary | setOfPubs | birthDate | 666 |
However, if evaluated, the following code would throw an exception.
baconArray at: 6 put: 'George'
An array is fixed size; it cannot be extended. The argument to at: must lie within the range of indexes that have been created. Furthermore, one cannot shrink an array by using remove:, but one can replace an element with another object. For example:
baconArray at: 1 put: 'The Old Devil'
replaces the string at index 1 with 'The Old Devil'. The message answer is the argument supplied to put:
baconArray includes: 'Francis Bacon'
returns true
baconArray isEmpty
returns false. Similarly
newArray := Array new: 10.
newArray isEmpty
returns false. The isEmpty message sends a size message that implements a check on the number of indexable fields in the receiver. In this case the size message produces an answer of 10 and consequently the isEmpty message produces a false message answer. Only when the number of stored elements equals 0 is true returned.
baconArray at: 3
returns setOfPubs, the textual representation of which is
Set('Dog and Duck' 'Colony Room' 'French House')
The indexOf: selector can be used like this:
baconArray indexOf: setOfPubs
and returns 3
The message selector to:do: in the protocol of Number can be used to initialise an array, as illustrated in the next scenario.
Next page » A scenario illustrating the use of Array
Previous page « Array
⇑ Up to top of page