mirror of
https://github.com/EiffelSoftware/eiffel-org.git
synced 2025-12-06 14:52:03 +01:00
5b930d3032
git-svn-id: https://svn.eiffel.com/eiffel-org/trunk@2469 abb3cda0-5349-4a8f-a601-0c33ac3a8c38
85 lines
2.7 KiB
Plaintext
85 lines
2.7 KiB
Plaintext
[[Property:title|Example: Self-initializing attributes and assigner commands]]
|
|
[[Property:weight|0]]
|
|
[[Property:uuid|dbc107a4-42cd-606a-71b2-e0b70ac5482e]]
|
|
==Description==
|
|
|
|
Example of using a [[Void-safety: Background, definition, and tools#Self-initializing attributes|self-initializing attribute]] and an [[ET: The Dynamic Structure: Execution Model#Assigner commands|assigner command]].
|
|
|
|
==Notes==
|
|
|
|
The concepts of [[Void-safety: Background, definition, and tools#Self-initializing attributes|self-initializing attributes]] and [[ET: The Dynamic Structure: Execution Model#Assigner commands|assigner commands]] are independent of one another. However, this example shows how each works in a small amount of code.
|
|
|
|
The example consists of two classes: a root class, and class <code>PERSON</code>. The <code>PERSON</code> class has a self-initializing attribute of type <code>STRING</code> named <code>mood</code>. If <code>mood</code> is accessed before it is explicitly initialized, then the self-initializing code after the keyword <code>attribute</code> will be executed, setting the default mood to "Happy".
|
|
|
|
The attribute <code>mood</code> also has an assigner command, the procedure <code>set_mood</code>, designated as such by the <code>assign</code> keyword. This allows clients of class <code>PERSON</code> to appear to assign directly to <code>mood</code>. However, the assigner command <code>set_mood</code> will always get executed, and its precondition will be in force during such an apparent assignment.
|
|
|
|
The root class <code>APPLICATION</code> creates an instance of <code>PERSON</code> and prints the value of <code>mood</code>, getting the self-iniitalized value. Then it assigns to <code>mood</code>. When it prints again, it gets the updated value.
|
|
|
|
==Source==
|
|
|
|
Adapted from an example given on the Eiffel Software Users Group.
|
|
|
|
==Solution==
|
|
|
|
A root class:
|
|
|
|
<code>
|
|
class
|
|
APPLICATION
|
|
|
|
create
|
|
make
|
|
|
|
feature {NONE} -- Initialization
|
|
|
|
make
|
|
-- Print and set mood of `my_person'.
|
|
do
|
|
create my_person
|
|
print ("Mood: " + my_person.mood + "%N")
|
|
my_person.mood := "Ecstatic"
|
|
print ("Mood: " + my_person.mood + "%N")
|
|
end
|
|
|
|
feature -- Access
|
|
|
|
my_person: PERSON
|
|
|
|
end
|
|
</code>
|
|
|
|
|
|
Class PERSON:
|
|
|
|
<code>
|
|
class
|
|
PERSON
|
|
|
|
feature -- Access
|
|
|
|
mood: STRING assign set_mood
|
|
attribute
|
|
Result := "Happy"
|
|
end
|
|
|
|
feature -- Element change
|
|
|
|
set_mood (a_string: STRING)
|
|
require
|
|
single_token: a_string.occurrences (' ') = 0
|
|
do
|
|
mood := a_string
|
|
ensure
|
|
mood_set: mood = a_string
|
|
end
|
|
end
|
|
</code>
|
|
|
|
==Output==
|
|
|
|
<code>
|
|
Mood: Happy
|
|
Mood: Ecstatic
|
|
</code>
|
|
|