From: blakemor@software.ORG (Alex Blakemore)
Subject: Re: derived types
Date: 23 Apr 89 15:33:24 GMT [thread overview]
Message-ID: <8904231604.AA02941@venera.isi.edu> (raw)
Re: 3.4.(15) and 7.4(4)
>> This disallows things like
>> type this is new integer;
>> type that is new this;
> The rationale behind this is due to the fact that a derived type receives
> it's parents subprograms. I.E. ALRM 3.4(13):
> The compiler will not know that all of these have been defined until
> it has finished compiling the spec. This insures that everything that must
> be derived for a new type is known.
OK, the above restrictions make it easier for compilers to make a single pass
over package specs. That alone may justify their inclusion in the reference manual.
Is that the only reason for these restrictions ?
Cascading the derivations across several packages is probably the best
solution but it does introduce other problems, esp if the base type is private.
See Bardin & Thompson's papers in Ada Letters, VIII, 1-2 for examples of
these problems and partial solutions if you're interested.
Alex Blakemore
Software Productivity Consortium
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