Re: Operator question.

Re: Operator question.

[Christoph Grein]

> What does the operator '=>' mean? I've been looking through my book
> "Programming in Ada95" but I cant seem to find it anywhere.

Just an addition to Martin Dowie's and Stephen Leake's explanation:

'=>' is not an operator, it is a delimiter (RM 2.2).

Operator question.

[Wannabe h4x0r]

Alright, forgive me if this question seems dumb. I cant beleive I havent
asked it before now.(or maybe I have and I just forgot.)

What does the operator '=>' mean? I've been looking through my book
"Programming in Ada95" but I cant seem to find it anywhere.

I see it everywhere in Ada code. Maybe I'm just a slow learner.

Any help would be appreciated.

Thanks.

Chris

Re: Operator question.

[Martin Dowie]

"Wannabe h4x0r" <chris@dont.spam.me> wrote in message
news:2vRa8.11975$kt5.28657@rwcrnsc52.ops.asp.att.net...
> Alright, forgive me if this question seems dumb. I cant beleive I havent
> asked it before now.(or maybe I have and I just forgot.)
>
> What does the operator '=>' mean? I've been looking through my book
> "Programming in Ada95" but I cant seem to find it anywhere.
>
> I see it everywhere in Ada code. Maybe I'm just a slow learner.

Me too ;-)

'=>' is use in a number of places, but really just to get a nice
readable syntax - it has no hidden value itself:

1. In named association e.g. the procedure call:
    Foo (Value => Bar);

   'Value' is the 'formal parameter name', 'Bar' is the 'actual parameter'

2. In case statements:
   case Value is
      when Foo =>
         ...
   end case;

3. In array assignment:
   Value : Array_Type := (1 .. 10 => 0);

4. In exception handlers:
   begin
      ...
   exception
      when My_Exception =>
         ...
   end;

There are probably others which I can't think of off the top of my
head.

Hope this helps.

Re: Operator question.

[Jerry Petrey]

Wannabe h4x0r wrote:
> 
> Alright, forgive me if this question seems dumb. I cant beleive I havent
> asked it before now.(or maybe I have and I just forgot.)
> 
> What does the operator '=>' mean? I've been looking through my book
> "Programming in Ada95" but I cant seem to find it anywhere.
> 
> I see it everywhere in Ada code. Maybe I'm just a slow learner.
> 
> Any help would be appreciated.
> 
> Thanks.
> 
> Chris


Actually Barnes first mentions the => (commonly called 'arrow') in his
section on array aggregates - he says it is akin to the 'pointing hand'
sign found in old railway timetables and used for indication directions.

Normally => is thought of as meaning 'gets' or 'becomes' as in the
subprogram call Foo (Value => X).  The formal parameter Value 'gets'
the actual parameter X and so forth.  In the case structure, it takes
on the 'pointing hand' analogy even better, i.e. 'for this case do this'.

Jerry
-- 
-----------------------------------------------------------------------------
-- Jerry Petrey                                                
-- Senior Principal Systems Engineer - Navigation, Guidance, & Control
-- Raytheon Missile Systems          - Member Team Ada & Team Forth
-- NOTE: please remove <NOSPAM> in email address to reply                  
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Re: Operator question.

[Stephen Leake]

Wannabe h4x0r <chris@dont.spam.me> writes:

> Alright, forgive me if this question seems dumb. I cant beleive I havent
> asked it before now.(or maybe I have and I just forgot.)
> 
> What does the operator '=>' mean? I've been looking through my book
> "Programming in Ada95" but I cant seem to find it anywhere.

Strictly speaking, "=>" is not an operator; it does not specify an
action performed on parameters, like "+" and "*" do. This may seem
like a nit, but it is very helpful to use correct terminology.

LRM 2.2 (14) says "=>" is called "arrow".

It is used for named association; it "associates" a parameter name
with the actual value in a subprogram call. For example:

procedure Foo (First, Last : in Integer);


Foo (First => 1, Last => 2);

This means the parameter 'First' gets the value 1, and 'Last' gets the
value 2. People often read "=>" as "gets".

Named association is also used in aggregates for records and arrays.
-- 
-- Stephe