Re: How to get this space away?

[Brad Moore <brad.moore@shaw.ca>]

On 2015-06-08 02:25 PM, Jeffrey R. Carter wrote:
> On 06/08/2015 12:47 PM, Randy Brukardt wrote:
>>
>> declare
>>      A_Img : constant String := Byte'Image(IP.A);
>>      B_Img : constant String := Byte'Image(IP.B);
>>      C_Img : constant String := Byte'Image(IP.C);
>>      D_Img : constant String := Byte'Image(IP.D);
>> begin
>>      Put (A_Img(2..A_Img'Last) & '.' & B_Img(2..B_Img'Last) & '.' &
>> C_Img(2..C_Img'Last) & '.' & C_Img(2..C_Img'Last);
>> end;

The version I was thinking of was

       Put (Strings.Fixed.Trim (Source => Byte'Image (IP(1)),
                                Side => Strings.Left) & '.' &
            Strings.Fixed.Trim (Source => Byte'Image (IP(2)),
                                Side => Strings.Left) & '.' &
            Strings.Fixed.Trim (Source => Byte'Image (IP(3)),
                                Side => Strings.Left) & '.' &
            Strings.Fixed.Trim (Byte'Image (IP(4)),
                                Side => Strings.Left));

Which is not that different in terms of readability.
A difference is that Randy's version required 4 declarations, where
this version can be written as an expression without any declarations.
I agree that for an IP Address one would probably want to encapsulate
the code in a library function. But for more general cases, sometimes
you need to construct similar output on the fly, and it is awkward
to have to write a function every time you want to do that.

It would have been quite a bit nicer to be able to write:

       Put (Byte'Image (IP(1)) & '.' & Byte'Image (IP(2)) & '.' &
            Byte'Image (IP(3)) & '.' & Byte'Image (IP(4));

But then if one wants zero padding, perhaps extending Text_IO to add some sort of Text_IO control
would be helpful, as in;

       Put (Byte'Image (IP(1)) & '.' & Text_IO.Pad('0') & Text_IO.Width(3) &
            Byte'Image (IP(2)) & '.' & Byte'Image (IP(3)) & '.' & Byte'Image (IP(4));


>
> I think you have C_Img in there twice.
>
>> Now, if you prefer to have each part to take up three characters with
>> leading zeros except for the first (so they're all the same length) --
>> that'll take a bit more than a handful of lines in Ada. Ada's formatting is
>> primitive, except in the rarely thought of Annex F (does anyone use that?).
>
> Presuming that "except for the first" means that IP.A should take up the minimum
> number of characters, as above:
>
> declare
>     function Image is new PragmARC.Images.Modular_Image (Number => Byte);
> begin
>     Put (Image (IP.A)                                  & '.' &
>          Image (IP.B, Width => 3, Zero_Filled => True) & '.' &
>          Image (IP.C, Width => 3, Zero_Filled => True) & '.' &
>          Image (IP.D, Width => 3, Zero_Filled => True) );
> end;
>
> And if you want IP.A to be 3 characters, zero filled, that's easy, too.
>

Yes, one could write their own routing or use a third party library such as this,
but it strikes me that such a capability should be built into the language.

Maybe the best answer is to standardize such a routine. I'm thinking it could fit
nicely into Ada.Strings.Fixed.

Brad