Re: incompatible assignement (POINTER TO LIMITED RECORD)

From: [at]} <HvL>
Date: Fri, 26 Oct 2007 16:05:31 +0200

----boundary-LibPST-iamunique-1527777672_-_-
Content-type: text/plain

I don't think so.
Assignment compatibility can only be allowed in cases, where the
structural identity of the variables is guaranteed forever, i. e.
statically; a dynamically enforced (type-)identity can of course not do
this.

H. v. L.

On Fri, 26 Oct 2007 15:44:15 +0200, Treutwein Bernhard
<Bernhard.Treutwein{([at]})nowhere.xy

> Gerald writes:
>
> [...]
>> This problem is not limited to... LIMITED records.
>> It's just that a^ and b^ are not assignment compatible.
>> As 'a' may be an extension of 'b' (at least in theory,
>> but I suppose the compiler doesn't verify this point),
>> 'a^' may be bigger than 'b^', so that the assignment is
>> impossible. If you remove the word 'LIMITED', there may
>> be no extension of 'Ball', and the problem vanishes.
>
> so I tried:
>
> b^ := a(Ball)^;
>
> but that yields also: "incompatible assignment" although the
> report says (in Sec. 8.1):
>
>
>> A type guard v(T) asserts that the dynamic type of
>> v is T (or an extension of T), i.e., program execution is
>> aborted, if the dynamic type of v is not T (or an extension
>> of T). Within the designator, v is then regarded as having
>> the static type T.
>
> which implies to me that the assignment should be possible.
>
> regards
> --
> Bernhard Treutwein, IuK, Ref. III A 3
> Bernhard.Treutwein(at)verwaltung uni-muenchen de
>
>
> ----
> To unsubscribe, send a message with body "SIGNOFF BLACKBOX" to
> LISTSERV{([at]})nowhere.xy

----
To unsubscribe, send a message with body "SIGNOFF BLACKBOX" to LISTSERV{([at]})nowhere.xy----boundary-LibPST-iamunique-1527777672_-_-
Content-type: application/rtf
Content-transfer-encoding: base64
Content-Disposition: attachment; filename="rtf-body.rtf"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----boundary-LibPST-iamunique-1527777672_-_---

Received on Fri Oct 26 2007 - 16:05:31 UTC