Re: Collective response to := messages

[dsr@hector.UUCP (David S. Rosenblum)]

In article <3720@hubcap.UUCP> billwolf@hubcap.clemson.edu writes:
|From article <10918@ulysses.homer.nj.att.com>, by dsr@hector.UUCP (David S. Rosenblum):
|> 
|> The ADT-handling package may feel like leaving a component undefined, but
|> Ada doesn't feel like leaving variables undefined after an assignment.
|> That's why such a user-defined assignment violates Ada's strong typing.
|
|      Really?  Consider the following:
|
|         procedure FUN_WITH_UNDEFINED_VARIABLES is
|
|            A : INTEGER;    -- A is undefined...
|            B : INTEGER;    -- B is undefined...
|         
|         begin
|            A := B;   -- Quick, what value does A have? 
|         end FUN_WITH_UNDEFINED_VARIABLES;

Easy.  A has a value that satisfies the constraints on INTEGER, which
implies that B does also.  We splitting hairs here, but I'll give it
to you--A is still undefined.

Note that you're relying on INTEGER being implicitly initialized with a valid
value; this is probably considered erroneous (I don't have an LRM
on hand).

|
|      This compiles and executes under Alsys Ada.

I don't doubt it.  Do you seriously regard this as "proof" that assignment
doesn't incorporate type checking?


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