-- card: 34473 from stack: in.07 Reference
-- bmap block id: 0
-- flags: 0000
-- background id: 13647
-- name: 


-- part 1 (field)
-- low flags: 00
-- high flags: 0002
-- rect: left=341 top=105 right=165 bottom=476
-- title width / last selected line: 0
-- icon id / first selected line: 0 / 0
-- text alignment: 0
-- font id: 3
-- text size: 9
-- style flags: 0
-- line height: 12
-- part name: 


-- part 2 (field)
-- low flags: 00
-- high flags: 0002
-- rect: left=341 top=168 right=269 bottom=475
-- title width / last selected line: 0
-- icon id / first selected line: 0 / 0
-- text alignment: 0
-- font id: 3
-- text size: 9
-- style flags: 0
-- line height: 12
-- part name: 


-- part 3 (field)
-- low flags: 00
-- high flags: 0002
-- rect: left=319 top=52 right=101 bottom=387
-- title width / last selected line: 0
-- icon id / first selected line: 0 / 0
-- text alignment: 0
-- font id: 3
-- text size: 9
-- style flags: 0
-- line height: 12
-- part name: 


-- part 5 (button)
-- low flags: 00
-- high flags: 8002
-- rect: left=323 top=287 right=308 bottom=445
-- title width / last selected line: 0
-- icon id / first selected line: 0 / 0
-- text alignment: 1
-- font id: 0
-- text size: 12
-- style flags: 0
-- line height: 16
-- part name: Attribute access
----- HyperTalk script -----
on mouseUp
  go to card id 36125
end mouseUp




-- part contents for background part 1
----- text -----
Pointers are used to access individual objects. Pointers 
are typed (or qualified) to reference a special class of 
objects. This means that it can point to objects of that 
class and any of its sub-classes. Many of the qualification
checks can be done during compilation but in some cases
the check has to be done during run-time.

It is possible to test the qualification of an object 
referenced by a pointer.  

The "is" construct will answer the question if an object 
is exactly of a specific qualification.

The "in" construct answers the question if an object 
belongs to a class or any of its sub-classes.


-- part contents for background part 2
----- text -----
Typed object pointers

-- part contents for card part 1
----- text -----
pa :- new A; ! -- OK;
pb :- new B; ! -- OK;
pa :- new B; ! -- OK;
pb :- new A; ! -- WRONG --;

-- part contents for card part 2
----- text -----
pa:- new B;

pa is A -- false
pa is B  -- true
pa in B  -- true
pa in A  -- Always true if
            -- pa =/= none

-- part contents for card part 3
----- text -----
class A;;
A class B;;
ref(A) pa;
ref(B) pb;