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Date: Wed, 1 May 2013 10:27:57 -0700 (PDT)
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Subject: Re: Ada 2012: In-out parameters for functions
From: Shark8 <onewingedshark@gmail.com>
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Date: 2013-05-01T10:27:57-07:00
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On Wednesday, May 1, 2013 10:28:07 AM UTC-6, dpt...@arcor.de wrote:
> 
> So, when do I use functions or procedures. Functions have return values. Any other differences?

Not really. Though a function w/ out parameters could be used like this:

-- Given Recognize(P : Pattern, S : String, O : out Object_Type) Return Boolean

if Recognize( Pattern_1, Input, Object ) then
 -- process object
elsif Recognize( Pattern_2, Input, Object ) then
 -- process object
end if;

Another thing is that functions can output unconstrained types [but the result is constrained], which means they can be used to assign to arrays or tagged-type 'CLASSes or the or discriminated types.

So we could now have a tokenizer like this:

-- Token_List: Vector containing the type Token.

Function Tokenize(Input : String) Return Token_List is
   -- Nested Tokenize consumes a portion of the string and returns a token.
   Function Tokenize(Input : in out Unbounded_String) Return Token
    with pre => Length(Unbounded_String) > 0;
   [...]
    Working : Unbounded_String:= To_Unbounded_String( Input );
begin
   Return Result : Token_List do
    while Length(Working) > 0 loop
      Result.Append( Tokenize(Working) );
    end loop;
   End return;
end Tokenize;