Hi Eric,
Don't know if I can help, but I agree that using attributes is not quite as
clear in the documentation as it might be (although there's an example of
validation on page 82 of the ooRexx Reference). Now I don't claim to be an
expert on attributes, but I do know that OO languages/software have many
ways of implementing the attribute concept. The ooRexx approach, once you
get used to it, is imho rather nice.
The following code aims to provide some examples of using attributes - both
defining them in a class called "MainlyAttributes" and getting/setting then
from outside the class. Each of the three attributes in the class is defined
slightly differently to indicate the range of options available. Hope this
helps.
/* Check out Attributes
A class with three attributes - x, y, and z, each specified differently:
x is fully spec'd using the ::attribute directive for both get and set.
Note the "set" code provided with the ::attribute directive. This code
constrains the value to be a numeric whole positive number and is taken
from the ooRexx Reference (page 82).
y uses the ::attribute statement for gets only; the set is provided as a
specific method called "y=". This method checks for numeric and returns
either .true or .false. Note that the returned value must be checked
using
the "result" special variable. If ,false is returned, the value of y is
set
to the string "Not Set".
z uses a single ::attribute directive with default get/set bevavior.
*/
i = .MainlyAttributes~new
say; say "-----------------Attributes Test----------------------------"
-- Get initial values of all three attributes:
say "Initial values of attributes assigned in the 'init' method:"
say "x=" i~x " y=" i~y " z=" i~z
say; say "Set x to 123 with the statement 'i~x = 123'."
i~x = 123
say "x is now:" i~x
say; say "Invoke a method that 'gets' all three attributes:"
i~getAllThree
say; say "Set y to an invalid value ..."
say "Invalid: i~y='abc'"
i~y='abc'
say "Result =" result
say "... and now to a valid value:"
say "Valid: i~y=100"
i~y=100
say "Result =" result
say; say "Set z to a different value using i~z='xyz'"
i~z='xyz'
say "z =" i~z
say; say "Set x to a valid numeric value using i~x=123"
i~x = 123;
say "i~x =" i~x
say; say "Set x to a non-numeric value. This will raise an error and exit."
say "But it's the last example in this program, so an exit here is OK."
i~x = "abc"
--
----------------------------------------------------------------------------
-
::class MainlyAttributes
::attribute x get
::attribute x set
expose x
use arg value
-- Prevent x having a value that is not a whole number by throwing an
error
-- and exiting if x is assigned a bad value:
if datatype(value, "Whole") = .false | value < 0 then
raise syntax 93.906 array ("x", value)
x = value
return 1
::attribute y get
::attribute z
::method init
expose x y z
x = 0
y = ""
z = "abc"
::method getAllThree
expose x y z
say "x =" x
say "y =" y
say "z =" z
::method "y=" -- equivalent to ::attribute y set
expose y
use arg a
if a~datatype("N") then do
y = a
return .true
end
y = ""
return .false
--
----------------------------------------------------------------------------
-
_____
From: Eric Davidson [mailto:eric-david...@bigfoot.com]
Sent: 28 December 2011 16:32
To: oorexx-users@lists.sourceforge.net
Subject: [Oorexx-users] ::attribute validation
As an ex-mainframe person who has been using REXX extensively for over 20
years, and using ooRexx procedurally for the last 5. I am trying to update
myself to develop code using the OO techniques.
I have read the documentation and I believe I understand the basics of
methods, but I am currently stuck using attributes - specifically how to
validate the values an attribute can have.
I can't seem to find simple examples of creating methods and validating.
Apologies if this is a basic question that I should have referred elsewhere
Eric Davidson
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