Re: Private function w/ Tagged return-type.

[Adam Beneschan <adambeneschan@aol.com>]

On Monday, July 29, 2013 1:54:40 PM UTC-7, Shark8 wrote:
> Given the following:
> 
> 
> 
> with Ada.Streams;
> package example is
>     Type Subject is tagged private;
>     function Create return Subject;
> private
>         function Input(
> 		    Stream : not null access Ada.Streams.Root_Stream_Type'Class)
> 	return  Subject is (Create);
> 
> ---- private, moved here, will work.
> 
>     Type Subject is tagged null record
>       with Input => Input;
> 
>     function Create return Subject is (null record);
> end example;
> 
> yields the following error message:
> 
>      private function with tagged result must override visible-part function
>      move subprogram to the visible part (RM 3.9.3(10))
> 
> Yet, the given paragraph says:
> 
>    For an abstract type declared in a visible part, an abstract primitive subprogram shall not be declared in the private part, unless it is overriding an abstract subprogram implicitly declared in the visible part. For a tagged type declared in a visible part, a primitive function with a controlling result or a controlling access result shall not be declared in the private part, unless it is overriding a function implicitly declared in the visible part.
> 
> Is the error correct? 'Input, 'Output, 'Read & 'Write are implicitly created due to the stream operations/attributes, though arguably they are not functions/subprograms.

Well, no matter which way you argue, the T'Input function does not have the name "Input" and will not be overridden by a function named "Input".

You can put your Input function in a nested package to avoid the error, since that will make it non-primitive.

                                 -- Adam