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From: "Gene" <gene.ressler@gmail.com>
Newsgroups: comp.lang.ada
Subject: Re: Surprise in array concatenation
Date: 5 Sep 2005 08:53:30 -0700
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Date: 2005-09-05T08:53:30-07:00
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Thanks for a great discussion.

I didn't say general array indexing is not useful; it obviously is. I
said it's marginally useful in the literal (economist's) sense of "at
the margin."  A few illustrations...

1) If one had to give up a feature in order to get another, many would
put general array indexing early on the chopping block. Between fixed
and dynamic length arrays (and in particular bounded/unbounded
strings), for example, Ada forces one to change from native array
syntax to a procedural interface that hides re-sizing details.  Ada
programmers I know would happily give up general index ranges in order
to get dynamically resizing arrays with native syntax---at least those
who have worked in other languages where such are available.

2) General integer ranges for array indices are a half-hearted---at the
margins---compromise wrt fully general arrays allowing any type as an
index.  In other words, if you put
(A) 1-based arrays,
(B) general discrete type array indices, and
(C) fully general arrays
on a conceptual scale, (B) lies _much_ closer to (A) than to (C).

3) The wonder of Ada is the predicatable, orthogonal way that syntax
and semantics correspond.  But we have just been observing that general
integer array indexing leads to a not-very-predictable behavior in
combination with slicing and catenation. If all arrays were 1-based,
the problem could not have occurred.  Hence this unhappy confluence of
features, by conflicting with Ada's philosophy, is at the semantic
margins of the language.  It ought to be avoided if the goal is code
with obvious meaning. E.g. after I re-coded my original example
"properly" with 'First and 'Range to make its behavior correct, I
quickly added a comment, -- 'First is not always 1.  How marginally
Ada!

Again best regards to all and thanks for the discussion.