Re: unsigned type

[Adam Beneschan <adam@irvine.com>]

On Jul 2, 6:42 pm, a...@anon.org (anon) wrote:
> --
> -- Just a side note.   Found while using a search engine.
> --
> with Ada.Text_IO ;
> use  Ada.Text_IO ;
>
> procedure Temp is
>
>     C : constant String := ( 1..0 => 'A' ) ;
>     --
>     --  So, what happens to the 'A' and why does the compiler allow
>     --  the constant 'A' when it result will be a null array.

Nothing happens to it.  This has been a known feature of Ada 83 and
Ada 95 forever; the only way to set up an empty array aggregate is to
provide a fake value.  It was particularly annoying when you had an
array of a record type; I often had to declare a useless dummy
variable of that record type just so I could say (1 .. 0 => Dummy).
There have been proposals to allow "null array" similar to the (null
record) aggregate, but they got nowhere.

Those proposals aren't needed any more anyway, since in Ada 2005 you
can say ( 1..0 => <> ) regardless of the element type.

>     --
>     --  If you use ( 1..0 => 'A' ) you must provide an unusable single
>     --  Character, double quotes or emply quote are illegal.  Logic
>     --  suggest that the statement should be
>     --  C : constant String := ( 1..0 => '' ) ;

Oh goodness.  The syntax '' doesn't mean anything in Ada, and this
would screw up every parser in the world because when they see two
single quotes together they think it's going to be a single '
character, i.e. '''.  Anyway, you can use <> so there's no longer any
need for a new syntax.

                        -- Adam