Trouble with "operation can be dispatching in only one type"

Trouble with "operation can be dispatching in only one type"

[Victor Porton]

I defined two tagged types T1 and T2 in some package.

I need a function in the same package:

not overriding function F (Stack: T1) return T2;

The compiler complaints:

operation can be dispatching in only one type

My current workaround is to define it instead as:

not overriding function F (Stack: T1'Class) return T2;

But this is a hack. Can I define this function in the right way? (I want it 
to be dispatching only in T1, not T2.)

-- 
Victor Porton - http://portonvictor.org

Re: Trouble with "operation can be dispatching in only one type"

[Victor Porton]

Victor Porton wrote:

> I defined two tagged types T1 and T2 in some package.
> 
> I need a function in the same package:
> 
> not overriding function F (Stack: T1) return T2;
> 
> The compiler complaints:
> 
> operation can be dispatching in only one type
> 
> My current workaround is to define it instead as:
> 
> not overriding function F (Stack: T1'Class) return T2;
> 
> But this is a hack. Can I define this function in the right way? (I want
> it to be dispatching only in T1, not T2.)

package Bad is

   type T1 is tagged null record;
   type T2 is tagged null record;

   not overriding function F (Stack: T1) return T2;
   
end Bad;

-- 
Victor Porton - http://portonvictor.org

Re: Trouble with "operation can be dispatching in only one type"

[Niklas Holsti]

On 14-08-13 22:23 , Victor Porton wrote:
> I defined two tagged types T1 and T2 in some package.
> 
> I need a function in the same package:
> 
> not overriding function F (Stack: T1) return T2;
> 
> The compiler complaints:
> 
> operation can be dispatching in only one type
> 
> My current workaround is to define it instead as:
> 
> not overriding function F (Stack: T1'Class) return T2;
> 
> But this is a hack. Can I define this function in the right way? (I want it 
> to be dispatching only in T1, not T2.)

To be dispatching in T1, but not in T2, it should be

   function F (Stack : T1) return T2'Class;

If the use of 'Class to prevent dispatching is a problem for you,
another way is to put the two type declarations in different packages.

A function F can be dispatching only in the type declared in the same
package as F. For example, if T2 is declared in a different package than
T1 (including a package nested within the package that declares T1) then
you can declare function F (Stack : T1) return Some_Pkg.T2 and it will
dispatch only in T1 (assuming that T1 and F are declared in the same
package declaration).

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
      .      @       .