Re: Records that could be arrays

Justin Gombos <rpbkbq.xax.gld@xxxxxxxx> writes:

I noticed this example code in 5.4.4 of the Ada Quality and Style
Guide:

type Coordinate is
record
Row : Local_Float;
Column : Local_Float;
end record;

type Window is
record
Top_Left : Coordinate;
Bottom_Right : Coordinate;
end record;

Would anyone here write something like that?

Yes; Windex has it. Although if I was rewriting it from scratch now,
I might use an array.

They are trying to illustrate that records should not always be flat,
which is a fine example for that purpose, but this seems to set a poor
example. Does anyone see a reason to use a record when an array can
be used? My version of the same structure would look more like:

type Axis is (Row, Column);
type Window_Vertex is (Top_Left, Bottom_Right);

type Coordinate is array (Axis) of Local_Float;
type Window is array (Window_Vertex) of Coordinate;

I have set a rule for myself: Composite types composed solely of one
type of element should be declared as arrays rather than records.
I've never seen this rule in a coding standard. The idea is that you
can be more expressive with an array. Example- there are more options
when it comes to an arrays role in control structures. Plus the
"others =>" notation is available. Thoughts?

I usually lean towards arrays, partly for the reasons you give, partly
because I have library utilities that work much more nicely with
arrays than records; Text_IO and containers for example. I can
create a Text_IO procedure Put for an array with a simple
instantiation; for a record, I have to use auto_text_io.

But records are deeply embedded in my psyche; these types just feel
more natural as records than arrays. I guess we need to catch the kids
in high school, and teach them to use arrays instead of records.

--
-- Stephe
.

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