From: Simon Wright <simon@pushface.org>
Subject: Re: Using 'Base
Date: Thu, 26 Jul 2012 18:21:56 +0100
Date: 2012-07-26T18:21:56+01:00 [thread overview]
Message-ID: <m2r4ryphe3.fsf@nidhoggr.home> (raw)
In-Reply-To: m2ipdhrsfr.fsf@nidhoggr.home
Simon Wright <simon@pushface.org> writes:
> I've been working on a binding to msgpack[1]; progress so far at [2],
> for booleans, integer, and modular types.
>
> Looking at the read-integer spec, I have
>
> with Ada.Streams;
> generic
> type Integer_Type is range <>;
> function Message_Pack.Integer_Reader
> (From : not null access Ada.Streams.Root_Stream_Type'Class)
> return Integer_Type'Base;
>
> and I _think_ that the point of returning the 'Base of the formal type
> is that any Constraint_Errors will happen in user code during
> assignment of the function result. The idea was copied from the
> Generic Elementary Functions, but I may well have got the reason
> wrong. And, also, I may still raise CE internally if the value
> received from the wire won't fit in Integer_Type'Base.
Quoting from the Ada 95 Rationale Part 3 Chapter A[3],
"The Ada 95 version uses Float_Type'Base as a type mark in
declarations; this was not available in Ada 83. Thus the formal
parameter types and result types of the functions are of the
unconstrained (base) subtype of the generic formal type Float_Type,
eliminating the possibility of range violations at the interface."
So I was correct.
> Is there any point in a similar declaration for write-integer? At
> present I have
But I still don't see why this is needed for _parameters_; if I supply
an out-of-range value for the generic formal type, shoudn't I be warned
at the call?
> with Ada.Streams;
> generic
> type Integer_Type is range <>;
> procedure Message_Pack.Integer_Writer
> (Stream : not null access Ada.Streams.Root_Stream_Type'Class;
> Item : Integer_Type'Base);
>
> (again, cf Generic Elementary Functions).
>
> [1] http://msgpack.org/
> [2] git://git.code.sf.net/u/simonjwright/msgpack-ada/code
[3]
http://www.adaic.org/resources/add_content/standards/95rat/rat95html/rat95-p3-a.html#3,
a bit over half way down
prev parent reply other threads:[~2012-08-01 2:52 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-07-21 16:26 Using 'Base Simon Wright
2012-07-26 17:21 ` Simon Wright [this message]
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