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Date: Wed, 02 Mar 2011 17:25:29 +0100
From: Georg Bauhaus <rm.dash-bauhaus@futureapps.de>
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Date: 2011-03-02T17:25:29+01:00
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On 02.03.11 16:40, Hyman Rosen wrote:

> What prevented the GNATColl authors from providing such an
> interface?

It may not always be possible.

Speaking more generally, there should be good reasons for
relying on string literals that represent structured information.
Such as calendar dates, which could easily be of a type other
than string, in any language supporting user defined, structured
types.

structure {
  .y = 2011,
  .m = 3,
  .d = 2
}

(I'll guess that PostgreSQL might let us define our own DATE
types, named differently, though.)

MySQL, for example, is very lenient. Sometimes in ways that
must lead to "erroneous execution".  You pass a value that is
not a valid value of the type.  An Ada compiler would tell you
in similar situations.  (So would a C compiler.) MySQL won't.
It might warn if you ask it.  But in "normal operation", it
continues with whatever it is programmed to substitute for
the incorrect value.

CREATE TEMPORARY TABLE T (TM TIME NOT NULL);

SELECT CAST('2011-02-02' AS DATE);

+----------------------------+
| 2011-02-02                 |
+----------------------------+

SELECT CAST('02-02-2011' AS DATE);

+----------------------------+
| NULL                       |
+----------------------------+

INSERT INTO T VALUES ('02-02-2011');
Query OK, 1 row affected, 1 warning (0.00 sec)

SELECT * FROM T;

+----------+
| 00:00:02 |
+----------+

INSERT INTO T VALUES ('02-02-2011');
Query OK, 1 row affected, 1 warning (0.00 sec)

SHOW WARNINGS;
+---------+------+-----------------------------------------+
| Warning | 1265 | Data truncated for column 'TM' at row 1 |
+---------+------+-----------------------------------------+

The fact that MySQL still drives many sites will neither bring back
the time spent fighting its leniency nor compensate for the amount
of anger created when confronted with its idiosyncrasies.
It is fast and cheap, though.  That's why it drives many sites.

A good (Ada) interface might try to provide a structured calendar
date type.  I doubt that such an interface will make the practical
programmer happy.