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Date: Thu, 17 Jun 2004 08:28:05 -0400
From: Hyman Rosen <hyrosen@mail.com>
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Subject: Re: Typing in Ada
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Date: 2004-06-17T08:28:05-04:00
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James Rogers wrote:
> One important difference between Ada records and C structs is
> in the creation of incomplete types. A C compiler allows the
> creation of incomplete types under the assumption that the
> type will be completed through the linking process, while an
> Ada compiler must have all types completed at compile time.

No, incomplete types in C have nothing to do with linking.
Incomplete types are there for the same reason as in any
other language, so that mutually recursive types may be
declared. Eg.,
     struct A;
     struct B { struct A *my_A; int x; };
     struct A { struct B *my_B; int y; };
For this mutual recursion to be possible, C and C++ must
then identify the places where incomplete types may be used,
such as in declarations of pointers to them, or as function
parameters - basically those places where knowing the innards
of the type is unnecessary.

It is true in C or C++ that if you never have a context in
which you need the complete type, you need not supply it,
even at link time.