Re: 'IMAGE

Re: 'IMAGE

[Mark A Biggar]

In article <1714@nic.cerf.net> sss@nic.cerf.net (Marlene M. Eckert) writes:
>Hello.
>Should the following 'image of an uninitialized
>enumeration type raise CONSTRAINT_ERROR?
>In similar situations our compiler has printed all
>blanks, garbage, and even readable garbage.  Of
>course, the answer is probably in the LRM somewhere...
>---------------------------------------------------------
>with Text_IO; use Text_IO;
>procedure Image is
>type Colors is (Red, Green, Blue);
>My_Color : Colors;  -- Not initialized!
>begin
>  Put_Line(Colors'image(My_Color)); -- Legal?
>end Image;

Using an undefined value like that makes your program erronious and it can do 
anything it damn well pleases, i.e., raise CONSTRAINT_ERROR, Crash the CPU,
Erase your hard disk, even as someone put it in comp.std.c in a similar
discussion cause miniture deamons to blow out your nose!

There has been quite a lot of discussion about this in the Ada9X reviewers
group and Ada9x may well contain something that tightens this up to at
least a bounded error (the program is still in error, it is not required that
the error be detected, but the set of allowed actions is finite and
specified by the standard.)

--
Mark Biggar
mab@wdl1.wdl.loral.com

Re: 'Image

[Björn Lundin]

On 2014-11-18 01:39, Randy Brukardt wrote:
> "Georg Bauhaus" <bauhaus@futureapps.invalid> wrote in message 
> news:m48b93$ke0$1@dont-email.me...
>> On 15.11.14 18:32, Florian Weimer wrote:
> ...
>> Will 'Image be user definable?
> 
> No, not in the Corrigendum (at least).

Is it conceptually the same as T'Image(varible) where T is a scalar type
? That is, it will not apply to records ?

--
Björn

Re: 'Image

[Randy Brukardt]

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"Björn Lundin" <b.f.lundin@gmail.com> wrote in message 
news:m4evds$bru$1@dont-email.me...
> On 2014-11-18 01:39, Randy Brukardt wrote:
>> "Georg Bauhaus" <bauhaus@futureapps.invalid> wrote in message
>> news:m48b93$ke0$1@dont-email.me...
>>> On 15.11.14 18:32, Florian Weimer wrote:
>> ...
>>> Will 'Image be user definable?
>>
>> No, not in the Corrigendum (at least).
>
> Is it conceptually the same as T'Image(varible) where T is a scalar type
> ? That is, it will not apply to records ?

Yes, exactly. Specifically:

 For a prefix X that denotes an object of a scalar type[ (after any implicit 
dereference)], the following attributes are defined:

X'Image  X'Image denotes the result of calling function S'Image with Arg 
being X, where S is the nominal subtype of X.

and similarly for Wide_Image and Wide_Wide_Image.

We've looked at ideas for allowing Image on record types, but it gets messy 
in a hurry, especially if user-defined Image is involved. (User-defined 
'Image only makes sense if there is some additional functionally associated 
with that, as in the stream case; otherwise, just defining a normal function 
is good enough [and fewer characters to write, too].)

                                Randy.

Re: 'Image

[G.B.]

On 19.11.14 14:46, Brian Drummond wrote:

> --------------------------------------------------------
> with Ada.Text_IO;
>
> procedure foo is
>      function "&" (l: string; r: natural) return string is
>      begin
>          return  l & character'VAL(r);
>      end "&";
>
>      a: constant string := "abcd";
>      b: constant string := "efgh";
> begin
>      Ada.Text_IO.put_line( "concatenated string is " & a &  -- Line 18
>              character'VAL(16#42#) & b &
>              "  " &  a & 16#42# & b );
> end foo;
> --------------------------------------------------------

This is from GNAT's Spitbol support package:

    function "&" (Num : Integer; Str : String)  return String;
    function "&" (Str : String;  Num : Integer) return String;
    function "&" (Num : Integer; Str : VString) return VString;
    function "&" (Str : VString; Num : Integer) return VString;
    --  In all these concatenation operations, the integer is converted to
    --  its corresponding decimal string form, with no leading blank.

Re: 'Image

[Brian Drummond]

On Wed, 19 Nov 2014 15:21:19 +0100, G.B. wrote:

> On 19.11.14 14:46, Brian Drummond wrote:
> 
>> --------------------------------------------------------
>> with Ada.Text_IO;
>>
>> procedure foo is
>>      function "&" (l: string; r: natural) return string is begin
>>          return  l & character'VAL(r);
>>      end "&";
...
> This is from GNAT's Spitbol support package:
> 
>     function "&" (Num : Integer; Str : String)  return String;
>     function "&" (Str : String;  Num : Integer) return String;
>     function "&" (Num : Integer; Str : VString) return VString;
>     function "&" (Str : VString; Num : Integer) return VString;
>     --  In all these concatenation operations, the integer is converted
>     to --  its corresponding decimal string form, with no leading blank.

heh, thanks!

- Brian