Re: Depending on passing mechanism

[kst@king.cts.com (Keith Thompson)]

Robert I. Eachus (eachus@spectre.mitre.org) wrote:
>  Ada 95 RM 6.2(4..10):
> 
>     "A type is a _by-reference_ type if it is a descendent of one of
> the following:
> 
>      ...
>      a nonprivate type with the reserved word limited in its declaration;
>      
>      a composite type with a subcomponent of a by-reference type;
> 
>      a private type whoes full type is a by-reference type;
> 
>      A parameter of a by-reference type is passed by reference..."
> 
>      To everyone other than Henry Baker this says that there is no
> problem of copy-in copy-out semantics in Ada 95 for limited private
> types since it isn't allowed.

Not quite, I'm afraid.  For example, type Foo in the following is
not a by-reference type:

   ...
      type Foo is limited private;
   private
      type Foo is
	 record
	    X : Integer;
	 end record;
   ...

To make it by-reference, you'd have to add the word "limited" to the
full type declaration.

This problem is acknowledged in AARM-6.2(10.g):

   We say "by-reference" above because these statements are not always
   true for limited private types whose underlying type is nonlimited
   (unfortunately).

-- 
Keith Thompson (The_Other_Keith) kst@cts.com <*>
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San Diego, California, USA
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