Containers - nontrivial element access

[Maciej Sobczak <see.my.homepage@gmail.com>]

I was thinking recently about what is wrong with the containers
interface. ;-)

Consider the following problem:
There is a record type (for example Person) with a couple of fields
(for example Salary) that together make the whole a bit heavy, so that
unnecessary copying of the whole is to be avoided. Objects of this
type are stored in the container.

I would like to swap salaries of two guys which I can refer with the
index/iterator/cursor/etc. The reference method is not really
important - what is important is the problem of modifying more than
one element in the container.

C++ example is easy:

vector<Person> people;
// ...
swap(people[x].salary, people[y].salary);

I hope it is obvious what it does (suppose x and y are some indices
into the vector). Just in case it isn't - all the components of the
two records stay intact except the salary, which is swapped between
the two. C++ makes it possible by explicitly returning a reference
from the method that accesses the element.

What would you suggest as the Ada solution for this problem?

The Update_Element procedure with its access to the user-provided
modifying procedure requires to pass data "under the table" (like with
a separate variable declared aside the modifying procedure) - and
seems to be just clunky. Is this the only possibility?

--
Maciej Sobczak * www.msobczak.com * www.inspirel.com