I am reading Markus Egger's "Advanced Object Oriented Programming
with Visual FoxPro 6.0". On page 335, he discusses derived
attributes/properties and gives some sample code. Unfortunately, it
is only a snippet.

I put something together myself. This works to the extent of
giving me the right answer.

Must I define c as a property? (If I have multiple derived
red-only properties, I would just as soon not define them.) Without
it, I get an error "Property C is not found." Is there another way to
do it? I looked at this_access, but the documentation is rather
opaque.

********** Start of Included Code **********
* Derived Property

o=createobject("derived")

o.a=3
o.b=4

? o.c

return

define class derived as custom

a=.f.
b=.f.
c=.f.

procedure c_access
return sqrt(this.a*this.a+this.b*this.b)
endproc

enddefine
********** End of Included Code **********

Sincerely,

Gene Wirchenko

Computerese Irregular Verb Conjugation:
I have preferences.
You have biases.
He/She has prejudices.

Since it's trying to print an object property (?o.c), then "c" must be a
property of that class. It must still be defined, even if you just give it
a default value. You can't have an _access method unless there's a property
for it to access!

--
Fred
Microsoft Visual FoxPro MVP


"Gene Wirchenko" <genew (AT) mail (DOT) ocis.net> wrote

"Fred Taylor" <ftaylor (AT) mvps (DOT) org!REMOVE> wrote:

Thank you. I was not totally sure.

Sincerely,

Gene Wirchenko

Computerese Irregular Verb Conjugation:
I have preferences.
You have biases.
He/She has prejudices.