User define attributes

User define attributes

[Ayende Rahien]

How do I add attributes to a type I create?

And how do I require certain attributes to be exist in a type? (I want a
generic package to accept only types that has 'Image attribute)

Thanks in advance,
Ayende Rahien

Re: User define attributes

[Martin Dowie]

don't think you can. I believe 'Image is available for all scalar types.
you could do something like

generic
  type Blah is private;
  function Image (X : Blah) return String;
package <...>;


Ayende Rahien <Dont@spam.me> wrote in message
news:9b9g7c$cp6$1@taliesin.netcom.net.uk...
> How do I add attributes to a type I create?
>
> And how do I require certain attributes to be exist in a type? (I want a
> generic package to accept only types that has 'Image attribute)
>
> Thanks in advance,
> Ayende Rahien
>
>

Re: User define attributes

[Ayende Rahien]

Okay, what abuot defining my own?

"Martin Dowie" <martin.dowie@nospam.baesystems.com> wrote in message
news:3ada9cf5$1@pull.gecm.com...
> don't think you can. I believe 'Image is available for all scalar types.
> you could do something like
>
> generic
>   type Blah is private;
>   function Image (X : Blah) return String;
> package <...>;
>
>
> Ayende Rahien <Dont@spam.me> wrote in message
> news:9b9g7c$cp6$1@taliesin.netcom.net.uk...
> > How do I add attributes to a type I create?
> >
> > And how do I require certain attributes to be exist in a type? (I want a
> > generic package to accept only types that has 'Image attribute)
> >
> > Thanks in advance,
> > Ayende Rahien
> >
> >
>
>

Re: User define attributes

[Martin Dowie]

well, if you mean someting like

type My_Type ...;
for My_Type'Image use ...;

you can't (that's for stream read/write only... I think), but as
attributes are defined as functions anyway (check annex L) you can
force your generic to require an Image function and even do nifty
instantiations like...

generic
  type My_Type is private;
  with function Image (X : My_Type) return String;
package Test is
  procedure Call (X : My_Type);
end Test;

with Test;
package Tester is new test (Integer, Integer'Image);


For composite types you have to "roll your own" Image routine that
would probably just call up the scalar 'Image routines in turn
or other rolled composite IMage routines.



Ayende Rahien <Dont@spam.me> wrote in message
news:9behk1$ik9$1@taliesin.netcom.net.uk...
> Okay, what abuot defining my own?
>
> "Martin Dowie" <martin.dowie@nospam.baesystems.com> wrote in message
> news:3ada9cf5$1@pull.gecm.com...
> > don't think you can. I believe 'Image is available for all scalar types.
> > you could do something like
> >
> > generic
> >   type Blah is private;
> >   function Image (X : Blah) return String;
> > package <...>;
> >
> >
> > Ayende Rahien <Dont@spam.me> wrote in message
> > news:9b9g7c$cp6$1@taliesin.netcom.net.uk...
> > > How do I add attributes to a type I create?
> > >
> > > And how do I require certain attributes to be exist in a type? (I want
a
> > > generic package to accept only types that has 'Image attribute)
> > >
> > > Thanks in advance,
> > > Ayende Rahien
> > >
> > >
> >
> >
>
>

Re: User define attributes

[Samuel T. Harris]

Martin Dowie wrote:
> 
> well, if you mean someting like
> 
> type My_Type ...;
> for My_Type'Image use ...;
> 
> you can't (that's for stream read/write only... I think), but as
> attributes are defined as functions anyway (check annex L) you can
> force your generic to require an Image function and even do nifty
> instantiations like...
> 
> generic
>   type My_Type is private;
>   with function Image (X : My_Type) return String;
> package Test is
>   procedure Call (X : My_Type);
> end Test;
> 
> with Test;
> package Tester is new test (Integer, Integer'Image);
> 
> For composite types you have to "roll your own" Image routine that
> would probably just call up the scalar 'Image routines in turn
> or other rolled composite IMage routines.
> 

It is trivial to build a generic which implements the a
width, value, and image function for arrays. All it needs
are the width, value, and image functions for the indexes
and composite types.

It is somewhat harder to build a generic for records
since the "index" are the field names and the composite
function depend upon which field is in use. But it
can be done.

I routinely write width, value, and image functions
for all my important types. Having these generics
in place, I get these routines with some simple
handler code and a generic instantiations. With them
I get the following advantages ...

1. I can easily insert put_line kinds of debug code.
2. If supported, I can call them within my debugger.
3. I can defer aggregrate initialization of variables
   to file_io during elaboration, and vice-versa.

-- 
Samuel T. Harris, Principal Engineer
Raytheon, Aerospace Engineering Services
"If you can make it, We can fake it!"

Re: User define attributes

[Martin Dowie]

been there; done that; got the compiler listing... :-)

I suspect there are many companies out there with very
similar generics.

I suppose we have to ask the question - if it is that
easy (and relative to the actual application, it
usually is!) then why isn't 'Image for composite types
part of the language?..

Samuel T. Harris <u61783@gsde.hou.us.ray.com> wrote in message
news:3ADB033A.F10344A9@gsde.hou.us.ray.com...
> It is trivial to build a generic which implements the a
> width, value, and image function for arrays. All it needs
> are the width, value, and image functions for the indexes
> and composite types.
>
> It is somewhat harder to build a generic for records
> since the "index" are the field names and the composite
> function depend upon which field is in use. But it
> can be done.
>
> I routinely write width, value, and image functions
> for all my important types. Having these generics
> in place, I get these routines with some simple
> handler code and a generic instantiations. With them
> I get the following advantages ...
>
> 1. I can easily insert put_line kinds of debug code.
> 2. If supported, I can call them within my debugger.
> 3. I can defer aggregrate initialization of variables
>    to file_io during elaboration, and vice-versa.

Re: User define attributes

[Brian Rogoff]

On Mon, 16 Apr 2001, Martin Dowie wrote:
> been there; done that; got the compiler listing... :-)

:-)

> I suspect there are many companies out there with very
> similar generics.
> 
> I suppose we have to ask the question - if it is that
> easy (and relative to the actual application, it
> usually is!) then why isn't 'Image for composite types
> part of the language?..

Given the desire to make array and function call syntax identical, I
wonder why there is even an attribute syntax at all, rather than just 
having function call syntax and system defined functions. I'd much rather 
just write Image(X) everywhere (but write A[I] for array access :). 

-- Brian
 
> Samuel T. Harris <u61783@gsde.hou.us.ray.com> wrote in message
> news:3ADB033A.F10344A9@gsde.hou.us.ray.com...
> > It is trivial to build a generic which implements the a
> > width, value, and image function for arrays. All it needs
> > are the width, value, and image functions for the indexes
> > and composite types.
> >
> > It is somewhat harder to build a generic for records
> > since the "index" are the field names and the composite
> > function depend upon which field is in use. But it
> > can be done.
> >
> > I routinely write width, value, and image functions
> > for all my important types. Having these generics
> > in place, I get these routines with some simple
> > handler code and a generic instantiations. With them
> > I get the following advantages ...
> >
> > 1. I can easily insert put_line kinds of debug code.
> > 2. If supported, I can call them within my debugger.
> > 3. I can defer aggregrate initialization of variables
> >    to file_io during elaboration, and vice-versa.
> 
> 
> 
> 

Re: User define attributes

[Samuel T. Harris]

Martin Dowie wrote:
> 
> been there; done that; got the compiler listing... :-)
> 
> I suspect there are many companies out there with very
> similar generics.
> 
> I suppose we have to ask the question - if it is that
> easy (and relative to the actual application, it
> usually is!) then why isn't 'Image for composite types
> part of the language?..
> 

I believe I asked that very same question here some
years ago. The response I got was the difficulty in
defining such a thing within the language and the
difficulties in implementing it in general. To which
I countered that the very same issues are relevant
to the definition and implementation of streams.
That is as far as the thread went (as far as my
imperfect memory recalls).

-- 
Samuel T. Harris, Principal Engineer
Raytheon, Aerospace Engineering Services
"If you can make it, We can fake it!"

Re: User define attributes

[Marin David Condic]

It seems reasonable to me to say that if you have to provide a translation
of a compound type into some stream of bytes (degenerating to the collective
internal representations of the primitive types plus index/discriminant
info) that adding a similar character representation ought to be near
trivial. When you get down to the bottom layer, instead of binary, you
translate to ASCII. Coming back in might be more difficult if you expect the
input to be user forgiving, but that shouldn't be any worse than calling the
'Value routines for the primitive types. Or an implementation is free to say
that the only thing guaranteed to work is Typename'Value(Typename'Image(X))?

Personally, I'd be at least mostly happy if the requirement were to give me
a dump of a compound structure from byte zero to byte N (plus the dope
information?) in various formats. (ASCII, hex, integer, etc.) This would
enable dumping the stuff out for debugging purposes which is usually the
reason I'd want a 'Image attribute for them anyway. (Rolling your own isn't
hard once you've got the object into a stream, but why not go for a
convenience feature?)

Most "real" outputs would want to be formatted in far more detail than I
could ever expect to get from a 'Image attribute anyway, so I wouldn't need
it except as a quick and dirty mechanism to see what is in the structure. It
is certainly handy for student-level programs. ('Image and 'Value are a lot
easier to explain than Text_IO when you just want to get someone rolling
with a "Hello World" program.) Or possibly for outputing a compound object
to a text file to be read back in at a later point? But then why not just
use Streams? (Maybe there should be a "Typename'Dump (X)" attribute with no
requirement other than the implementation provide some kind of human
readable text for the contents of X?)

MDC
--
Marin David Condic
Senior Software Engineer
Pace Micro Technology Americas    www.pacemicro.com
Enabling the digital revolution
e-Mail:    marin.condic@pacemicro.com
Web:      http://www.mcondic.com/


"Samuel T. Harris" <u61783@gsde.hou.us.ray.com> wrote in message
news:3ADB1BAA.6F4E0437@gsde.hou.us.ray.com...
> I believe I asked that very same question here some
> years ago. The response I got was the difficulty in
> defining such a thing within the language and the
> difficulties in implementing it in general. To which
> I countered that the very same issues are relevant
> to the definition and implementation of streams.
> That is as far as the thread went (as far as my
> imperfect memory recalls).
>

Re: User define attributes

[Samuel T. Harris]

Marin David Condic wrote:
> 
> It seems reasonable to me to say that if you have to provide a translation
> of a compound type into some stream of bytes (degenerating to the collective
> internal representations of the primitive types plus index/discriminant
> info) that adding a similar character representation ought to be near
> trivial. When you get down to the bottom layer, instead of binary, you
> translate to ASCII. Coming back in might be more difficult if you expect the
> input to be user forgiving, but that shouldn't be any worse than calling the
> 'Value routines for the primitive types. Or an implementation is free to say
> that the only thing guaranteed to work is Typename'Value(Typename'Image(X))?

My functions, and my original question, dealt with Ada's
aggregate with named notation. Specifically qualified aggregates
where the full type name and a "'" preceeds the aggregate.

> 
> Personally, I'd be at least mostly happy if the requirement were to give me
> a dump of a compound structure from byte zero to byte N (plus the dope
> information?) in various formats. (ASCII, hex, integer, etc.) This would
> enable dumping the stuff out for debugging purposes which is usually the
> reason I'd want a 'Image attribute for them anyway. (Rolling your own isn't
> hard once you've got the object into a stream, but why not go for a
> convenience feature?)

Of course, aggregates using named notation have no need for
dope vectors. Record discriminants come first so no problem there.
By using qualified aggregates, even complications introduced by
tagged types are trivially handled.

> 
> Most "real" outputs would want to be formatted in far more detail than I
> could ever expect to get from a 'Image attribute anyway, so I wouldn't need
> it except as a quick and dirty mechanism to see what is in the structure. It
> is certainly handy for student-level programs. ('Image and 'Value are a lot
> easier to explain than Text_IO when you just want to get someone rolling
> with a "Hello World" program.) Or possibly for outputing a compound object
> to a text file to be read back in at a later point? But then why not just
> use Streams? (Maybe there should be a "Typename'Dump (X)" attribute with no
> requirement other than the implementation provide some kind of human
> readable text for the contents of X?)

I don't need "real" outputs. I just want convenient output
for anything I want, in function form suitable to be called
directly from the debugger. By standardizing on Ada aggregate
notation, I can even switch output with source code and source
code as input. I even handle pointers in a portable manner.

One of the inconveniences in my experience with using streams
or other binary representation for transmission is that I
cannot simply use a network sniffer to spoof the contents.
If I'm passing all data packets with textual contents, I can
read what a distributed system is doing with any old spoofer.


-- 
Samuel T. Harris, Principal Engineer
Raytheon, Aerospace Engineering Services
"If you can make it, We can fake it!"

Re: User define attributes

[Georg Bauhaus]

Samuel T. Harris (u61783@gsde.hou.us.ray.com) wrote:

: One of the inconveniences in my experience with using streams
: or other binary representation for transmission is that I
: cannot simply use a network sniffer to spoof the contents.
: If I'm passing all data packets with textual contents, I can
: read what a distributed system is doing with any old spoofer.

So you could write your own 'Write or 'Output and
use text streams. Am I missing something?


Georg

Re: User define attributes

[Samuel T. Harris]

Georg Bauhaus wrote:
> 
> Samuel T. Harris (u61783@gsde.hou.us.ray.com) wrote:
> 
> : One of the inconveniences in my experience with using streams
> : or other binary representation for transmission is that I
> : cannot simply use a network sniffer to spoof the contents.
> : If I'm passing all data packets with textual contents, I can
> : read what a distributed system is doing with any old spoofer.
> 
> So you could write your own 'Write or 'Output and
> use text streams. Am I missing something?

My prior effort was for Ada 83, no streams.

While what you suggest would work, there is a lot more
overhead to setting up streams.

And it doesn't address my original question, if the
mechanism was in place to define streams, why is it
not in place for image/value/width?

-- 
Samuel T. Harris, Principal Engineer
Raytheon, Aerospace Engineering Services
"If you can make it, We can fake it!"

Re: User define attributes

[Samuel T. Harris]

Georg Bauhaus wrote:
> 
> Samuel T. Harris (u61783@gsde.hou.us.ray.com) wrote:
> 
> : One of the inconveniences in my experience with using streams
> : or other binary representation for transmission is that I
> : cannot simply use a network sniffer to spoof the contents.
> : If I'm passing all data packets with textual contents, I can
> : read what a distributed system is doing with any old spoofer.
> 
> So you could write your own 'Write or 'Output and
> use text streams. Am I missing something?
> 
> Georg

Yes, read what I wrote before.

My original concept was year ago way before Ada 95.
Even with Ada 95, streams have additional overhead.

And this does not address my original question of
why are streams smart and image/value isn't.

-- 
Samuel T. Harris, Principal Engineer
Raytheon, Aerospace Engineering Services
"If you can make it, We can fake it!"

Re: User define attributes

[Martin Dowie]

great minds...  :-)

I can see how the actual output may vary from compiler to
compiler, but that sort of problem crops up all over the
place. If the RM had put a few examples in it should have
been _that_ hard? should it?

Samuel T. Harris <u61783@gsde.hou.us.ray.com> wrote in message
news:3ADB1BAA.6F4E0437@gsde.hou.us.ray.com...
> I believe I asked that very same question here some
> years ago. The response I got was the difficulty in
> defining such a thing within the language and the
> difficulties in implementing it in general. To which
> I countered that the very same issues are relevant
> to the definition and implementation of streams.
> That is as far as the thread went (as far as my
> imperfect memory recalls).

Re: User define attributes

[Martin Dowie]

Is consistency such a big deal - if so, then it seems that it
is streams that are being inconsistent... ;-)


Ted Dennison <dennison@telepath.com> wrote in message
news:0tEC6.7646$FY5.638172@www.newsranger.com...
> That would be consistent with what is done with streams. But to enhance
the
> consistency, you'd want 'Image on aggregate to do a 'Image on each
component,
> and for that to work you'd want 'Image defined on *everything*.

Re: User define attributes

[Marius Amado Alves]

On Mon, 16 Apr 2001, Samuel T. Harris wrote:
> It is somewhat harder to build a generic for records
> since the "index" are the field names and the composite
> function depend upon which field is in use. But it
> can be done.

It can?  You mean without passing the names of the components explicitly,
parallelely?  Please let us know how!

I am really curious because some months ago this was briefly discussed
here on CLA and the conclusion was negative.  Not even a compiler
dependent means was detected.

-- 
Marius Amado Alves
 alves@systran.lu
Project Tradaut-Pt
Systran Luxembourg
12, Rue de Vianden
L-2680  LUXEMBOURG
Tel 352 + 45 46 53
Fax 352 + 45 74 75

Re: User define attributes

[Samuel T. Harris]

Marius Amado Alves wrote:
> 
> On Mon, 16 Apr 2001, Samuel T. Harris wrote:
> > It is somewhat harder to build a generic for records
> > since the "index" are the field names and the composite
> > function depend upon which field is in use. But it
> > can be done.
> 
> It can?  You mean without passing the names of the components explicitly,
> parallelely?  Please let us know how!
> 
> I am really curious because some months ago this was briefly discussed
> here on CLA and the conclusion was negative.  Not even a compiler
> dependent means was detected.
> 

Lets go back to the array. It needs generic formal parameters
for the width, image, and value of its index type and its
component type. An instantiation provides a width, image, and
value function for the composite type (i.e. the array).
This is easy because an array is a homogenous collection.
No matter the value of the index, the handling of components
are the same.

Now, compare this to records. Records are a heterogenous
collection. The handling of components depends upon
which component one is dealing. So, the image, value,
and width functions for the components must case
off of the field name and defer to the appropriate
field type. This case you have to write in preparation
for you instantiation. Some code examples follow ...

Here is the spec for a generic which supports arrays.

    generic
	type Index_Type is (<>);
	type Component_Type is private;
	type Array_Type is array (Index_Type range <>) of Component_Type;
	with function Width (Item : Index_Type) return Natural is <>;
	with function Image (Item : Index_Type) return String is <>;
	with function Value (Item : String) return Index_Type is <>;
	with function Width (Item : Component_Type) return Natural is <>;
	with function Image (Item : Component_Type) return String is <>;
	with function Value (Item : String) return Component_Type is <>;
    package Array_Attribute_Functions is
	-- The base type of the generic index_type must have a predecessor to
	-- index_type'first to support returning the value of an empty image "()".
	function Width (Item : Array_Type) return Natural;
	function Image (Item : Array_Type) return String;
	function Value (Item : String) return Array_Type;
    end Array_Attribute_Functions;

And here is an instantiation ...

  type Test_Record_Array is array (Positive range <>) of Test_Record_Type;

  function Width (Item : Positive) return Natural;

  function Image (Item : Positive) return String;

  function Value (Item : String) return Positive;

  function Width (Item : Test_Record_Type) return Natural 
    renames Test_Record_Type_Attributes.Width;

  function Image (Item : Test_Record_Type) return String 
    renames Test_Record_Type_Attributes.Image;

  function Value (Item : String) return Test_Record_Type 
    renames Test_Record_Type_Attributes.Value;

  package Test_Record_Array_Attributes is 
    new Array_Attribute_Functions 
     (Index_Type => Positive,
      Component_Type => Test_Record_Type,
      Array_Type => Test_Record_Array);

... where I could have used positive'image and positive'value
for the index functions, but I cannot use positive'width
since it is a parameterless function. I have to define a width
function which is a simple one-liner. So, for consistency I
also define an image and value function. Ignore, for the moment,
the fact that with width, image, and value functions for the
record type have not been defined yet, that will come later.

I believe the implementation of the generic body is obvious
to most everyone. Image simply iterates over the index of
the parameter and calls the image of the index and the
image of the component, puts a "=>" finger in between,
adds a separating "," after each iteration, except the last.
Finally it decorates the whole thing with enclosing "()".

The necessary code to satisfy the generic instantiation
is trivial for arrays. Now lets look at records ...

   generic
	type Field_Type is (<>);
	type Record_Type is private;
	-- Record fields should all have default values.
	with function Width (Item : Field_Type) return Natural is <>;
	with function Image (Item : Field_Type) return String is <>;
	with function Value (Item : String) return Field_Type is <>;
	-- Width of a field of the record with default value
	-- must represent the largest width possible.
	with function Width (Field : Field_Type; Item : Record_Type)
			    return Natural is <>;
	with function Image (Field : Field_Type; Item : Record_Type)
			    return String is <>;
	with procedure Value (Item : String;
			      Field : Field_Type;
			      Into : in out Record_Type) is <>;
    package Record_Attribute_Functions is
	function Width (Item : Record_Type) return Natural;
	function Image (Item : Record_Type) return String;
	function Value (Item : String) return Record_Type;
    end Record_Attribute_Functions;

... which look much like the one for arrays with the following
differences.

1. Instead of an index type, we have a field type.
2. Width, Image, and Value functions dealing with the component
   have a field_type parameter. The corresponding array function
   did not since the array generic know how to index the array
   but the record generic cannot "index" the record by field.
3. Instead of a component value function, we have a
   value procedure which works on the composite type.

The need for a value procedure is obvious when one considers
that various fields may have various types and their is no
way for a single value function to support those various
types. So, instead of providing a value function, the coder
must prepare a value procedure which incrementally fills
in a working record kept by generic body.

Here is an instantiation which provided the width, image,
and value function for the array generic ...

  type Test_Record_Type is
    record
      I, J : Largest_Integer;
      X, Y, Z : Largest_Float;
    end record;

  type Test_Record_Field is (I, J, X, Y, Z);

  function Width (Item : Test_Record_Field) return Natural;
  function Image (Item : Test_Record_Field) return String;
  function Value (Item : String) return Test_Record_Field;
  function Width (Field : Test_Record_Field; Item : Test_Record_Type) return Natural;
  function Image (Field : Test_Record_Field; Item : Test_Record_Type) return String;
  procedure Value (Item : String; Field : Test_Record_Field; Into : in out Test_Record_Type);

  package Test_Record_Type_Attributes is
    new Record_Attribute_Functions
     (Test_Record_Field, Test_Record_Type);

... The body of width, image, and value which involve
components must handle the "indexing" of field names
to actual record components. This is most easily done
with case statements where each field alternative
calls the appropriate width, image, or value function
according to the field types. Each field for image
and value will have its own alternative. Normally
the width will also have one alternative per field.

As a side note for discriminent and variant records,
the discriminants should come first. The value
function cannot determine the actual type of the
return value until it has all discriminants. This
means all discriminant need to have default values
to allow record variables to polymorph. The value
function simply resets the in out parameter when
it know it has all the other discriminants.

All three subprograms; width, image, and value;
may employ sophisticated logic to handle variant
records in order to avoid access invalid fields
as they interate over the "index" field_type.
Or they can just simply make the attempt and
handle constraint_error with a very localized
null exception handler.

I hope that answers your questions.
Since this code was written for a particular
project, I am not free to release the contents.
However, if there is some demand, I shall
rewrite it from scratch at home and submit
it to www.adapower.com.

-- 
Samuel T. Harris, Principal Engineer
Raytheon, Aerospace Engineering Services
"If you can make it, We can fake it!"

Re: User define attributes

[Jeffrey Carter]

"Samuel T. Harris" wrote:
> 
>     generic
>         type Index_Type is (<>);
>         type Component_Type is private;
>         type Array_Type is array (Index_Type range <>) of Component_Type;
>         with function Width (Item : Index_Type) return Natural is <>;
>         with function Image (Item : Index_Type) return String is <>;
>         with function Value (Item : String) return Index_Type is <>;

Note that since Index_Type is a discrete type, the generic can call
Index_Type'Image, Index_Type'Value, and so on directly.

-- 
Jeff Carter
"You couldn't catch clap in a brothel, silly English K...niggets."
Monty Python & the Holy Grail

Re: User define attributes

[Samuel T. Harris]

Jeffrey Carter wrote:
> 
> "Samuel T. Harris" wrote:
> >
> >     generic
> >         type Index_Type is (<>);
> >         type Component_Type is private;
> >         type Array_Type is array (Index_Type range <>) of Component_Type;
> >         with function Width (Item : Index_Type) return Natural is <>;
> >         with function Image (Item : Index_Type) return String is <>;
> >         with function Value (Item : String) return Index_Type is <>;
> 
> Note that since Index_Type is a discrete type, the generic can call
> Index_Type'Image, Index_Type'Value, and so on directly.
> 

Reread my post. I address that issue. Width cannot be assumed,
due to the other kinds of generics I have written (like
address_attribute_functions) so it must be "functionized"
in certain places, so I functionize it in all places.
Similarly for image and value. It is there for the sake
on consistency.

Besides, I may want to instantiate this generic with something
other than the attribute functions or their equivalent.
I might want some particular format, even for integers
or floats (like say using base 16 instead of base 10).

My general rule on generics is pass in all functionality and
default then to "is <>". This includes numerics. Generics
involving numeric types should pass in all the operators.
This notion is especially important when one considers
that limited private types with a new equality operator
defined will revert back to the default equality
in generic instantiations. Better to pass that "=" in.
Since these are usually defaulted for me, I don't
both providing in the generic instantiation. I only
have to bother with ensuring they are visible with
appropriate use clauses.

-- 
Samuel T. Harris, Principal Engineer
Raytheon, Aerospace Engineering Services
"If you can make it, We can fake it!"

Re: User define attributes

[Marius Amado Alves]

On Wed, 18 Apr 2001, Samuel T. Harris wrote:
> 
>     generic
> 	type Index_Type is (<>);
> 	type Component_Type is private;
>       ...
>     package Array_Attribute_Functions is
> 	function Width (Item : Array_Type) return Natural;
> 	function Image (Item : Array_Type) return String;
> 	function Value (Item : String) return Array_Type;
>     end Array_Attribute_Functions;
>
> ...

My package Bundles is along those lines.

generic

  type Names is (<>);

package Bundles is

  type Bundle_Type is array(Names) of Unbounded_String;

  function Bundle(
    S: String;
    Indicator: String := "=>";
    Separator: String := ",")
    return Bundle_Type;
      -- Parses a bundle representation S into a Bundle_Type.
      -- White space between tokens is ignored.
      -- Unnamed items are assigned Null_Unbounded_String.
      -- B = Bundle(Image(B)) holds.

  function Image(
    ...

It has served me long and well.

It is now in Adlib (lexis.di.fct.unl.pt/ADaLIB), category Miscelany.

--
Marius Amado Alves
 alves@systran.lu
Project Tradaut-Pt
Systran Luxembourg
12, Rue de Vianden
L-2680  LUXEMBOURG
Tel 352 + 45 46 53
Fax 352 + 45 74 75
Mob 351 +939354002