Re: Ada Idioms Progress Preview

[Ole-Hjalmar Kristensen <ohk@clustra.com>]

Ted Dennison<dennison@telepath.com> writes:

> In article <3_Xc7.45$NM5.84779@news.pacbell.net>, Jay Nabonne says...
> >
> >useful for me - and it's what I thought of when I saw the word idiom - is
> >something that says "in order to do <blah>, given that there's more than one
> >way to do it within the Ada language, here's how you write code that looks
> >like an Ada programmer wrote it and doesn't look like a
> >C++-programmer-writing-Ada wrote it.".
> >
> >I'm interested in how to "think in Ada"...
> 
> The best advice I can give you today is to go to the Ada Source Code Treasury at
> http://www.adapower.com/adacode.html . The master site itself is useful too.
> 
> Based on my experience with native C speakers, here are some basic things to get
> you started:
> 
> o  Strings in Ada are *very* different from Strings in C. Ada strings end at the
> end of the array (or slice of it you specify), not at some arbitrarily-chosen
> "terminator" character. Look into the "&" operator for arrays, and the array
> attributes 'length, 'first, and 'last. 'image is damn nice too. Don't be
> discouraged if you have trouble with this seemingly simple thing. Conceptually,
> this is probably the biggest difference the languages have.

One thing which can be said in favour of having a terminator character
is that it frees you from having to store the length explicitly. The
length of a string is usually different from the size of the array
used to store the string.
So, in a sense a C string is more self-describing than a plain Ada
string. 
Of course, as soon as you call a procedure, you can use a slice, but
you still need the actual length to decide which slice.

On the balance, I would rather have Ada strings.

> 
> o  The techniques you learn for dealing with strings can be used for *all*
> arrays.
> 
> o  Make yourself familiar with the language defined attributes (
> http://www.ada-auth.org/~acats/arm-html/RM-K.html ).
> 
> o  Passing a large data structure as a parameter does *not* mean that the whole
> thing gets copied. The compiler will internally pass a reference to the
> structure if that would be more efficient. Do *not* use pointers yourself to
> force this effect.
> 
> o  You almost never need pointers.
> 
> o  If you think you need a pointer, see the previous point. :-)
> 
> ---
> T.E.D.    homepage   - http://www.telepath.com/dennison/Ted/TED.html
>           home email - mailto:dennison@telepath.com

-- 
Kabelsalat ist gesund.

Ole-Hj. Kristensen