From: mbk@inls1.ucsd.edu (Matt Kennel)
Subject: Re: Mut. Recurs. in Ada9X w/o Breaking Encaps.? (LONG)
Date: 30 Sep 1994 22:46:03 GMT
Date: 1994-09-30T22:46:03+00:00 [thread overview]
Message-ID: <36i4fb$hsn@network.ucsd.edu> (raw)
In-Reply-To: 1994Sep29.133526.2134@swlvx2.msd.ray.com
John Volan (jgv@swl.msd.ray.com) wrote:
: Not true. The premise of my original question was that the binary association
: between Employee and Office is a public feature fully visible to their
: clients -- and they could even include each other as clients! Maybe the
: *implementation* of this binary association is strictly internal to the
: abstraction (I agree that it should be), but the *existence* of this binary
: association should be a visible part of this abstraction. In other words,
: the interface to the Employee class should include some subprogram(s) that
: allow(s) a client to fetch the identity of (a pointer to) the associated Office.
: Likewise the interface to the Office class should include some subprogram(s)
: that allow(s) a client to fetch the identity of (a pointer to) the associated
: Employee. And the interface to both classes should include some subprogram(s)
: that allow a client to establish an association between a given Office and a
: given Employee, in such a way as to always guarantee the following invariant
: assertion:
: For any given Employee "E" and Office "O",
: E occupies O if and only if O is occupied by E.
How about this kind solution? I'm going to have to write in ersatz
Eiffel/Sather:
class TWO_WAY_RELATION{T1,T2} is
private map_1_to_2:MAP{T1,T2}; -- MAP{T1,T2} is a hash table
-- data structure that finds T2's given
-- T1's as keys.
private map_2_to_1:MAP{T2,T1};
create is
map_1_to_2 := #MAP{T1,T2};
map_2_to_1 := #MAP{T1,T2}; end;
add_pair(x:T1,y:T2) is
map_1_to_2.insert(x,y);
map_2_to_1.insert(y,x);
end;
find_one_given_two(y:T2):T1 is
return map_2_to_1.find(y); end;
find_one_given_two(x:T1):T2 is
return map_1_to_2.find(x); end;
end; -- class TWO_WAY_RELATION
class EMPLOYEE is
private shared mapper:TWO_WAY_RELATION{EMPLOYEE,OFFICE};
-- shared so all instances access the same object
find_my_office : OFFICE is
mapper.find_two_given_one(self); end;
set_my_office(o:OFFICE) is
mapper.add_pair(self,o); end;
end; -- EMPLOYEE
class OFFICE is
private shared mapper:TWO_WAY_RELATION{EMPLOYEE,OFFICE}
-- shared so all instances access the same object
find_my_employee : OFFICE is
mapper.find_one_given_two(self); end;
set_my_employee(e:EMPLOYEE) is
mapper.add_pair(e,self); end;
end; -- OFFICE
---
Now, both Office and Employee present interfaces that can find
and set each one's counterpart. Neither knows how to do this
except through the 'mapper' object, which presents a clean interface
for managing pairs.
Comments?
--
-Matt Kennel mbk@inls1.ucsd.edu
-Institute for Nonlinear Science, University of California, San Diego
-*** AD: Archive for nonlinear dynamics papers & programs: FTP to
-*** lyapunov.ucsd.edu, username "anonymous".
next prev parent reply other threads:[~1994-09-30 22:46 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
1994-09-27 16:52 Mut. Recurs. in Ada9X w/o Breaking Encaps.? (LONG) John Volan
1994-09-27 18:48 ` Mark A Biggar
1994-09-29 1:46 ` John Volan
1994-09-29 13:57 ` Tucker Taft
1994-09-29 17:20 ` Bjarne Stroustrup <9758-26353> 0112760
1994-09-30 1:38 ` Tucker Taft
1994-09-30 12:33 ` Bjarne Stroustrup <9758-26353> 0112760
1994-09-29 18:37 ` John Volan
1994-09-29 19:34 ` David Weller
1994-09-30 22:13 ` John Volan
1994-10-02 3:31 ` Andrew Lees
1994-09-30 1:47 ` Tucker Taft
1994-09-30 13:30 ` John Volan
1994-09-29 18:10 ` R. William Beckwith
1994-10-03 0:33 ` Cyrille Comar
1994-09-28 14:01 ` Norman H. Cohen
1994-09-29 2:12 ` John Volan
1994-09-29 14:01 ` Tucker Taft
1994-09-29 18:37 ` Norman H. Cohen
1994-09-29 9:48 ` Magnus Kempe
1994-09-29 13:10 ` Magnus Kempe
1994-09-29 18:05 ` Tucker Taft
1994-09-30 10:20 ` Mut. Recurs. in Ada9X w/o Breaking Encaps.? Magnus Kempe
1994-09-30 13:22 ` Tucker Taft
1994-10-01 1:24 ` Mut. Recurs. in Ada9X w/o Breaking Encaps.? (LONG) Adam Beneschan
1994-10-01 12:01 ` Magnus Kempe
1994-10-01 18:43 ` Mark A Biggar
1994-10-02 16:41 ` John Volan
1994-10-02 23:33 ` Matt Kennel
1994-10-03 8:07 ` Mut. Recurs. in Ada9X w/o Breaking Encaps.? Magnus Kempe
1994-10-03 12:14 ` Mut. Recurs. in Ada9X w/o Breaking Encaps.? (LONG) Robert I. Eachus
1994-10-04 2:12 ` R. William Beckwith
1994-10-04 16:00 ` John Volan
1994-10-05 11:42 ` Robert I. Eachus
1994-10-05 21:09 ` Matt Kennel
1994-10-03 20:29 ` Harry Koehnemann
1994-09-29 13:35 ` John Volan
1994-09-30 20:27 ` Norman H. Cohen
1994-10-01 1:47 ` John Volan
1994-10-01 20:44 ` Tucker Taft
1994-10-03 11:29 ` Robert I. Eachus
1994-09-30 22:46 ` Matt Kennel [this message]
1994-10-01 2:11 ` John Volan
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