Re: Prefix to 'ACCESS must either statically match... But why?

[Vadim Godunko <vgodunko@vipmail.ru>]

Wojtek Narczynski wrote:
> 
> Could somebody please explain me why is this rule present? I find it
> very limting. Is this because AR2 bounds are not stored with the
> object?
> 
> Type Stream_Element_Array_access is access all Stream_Element_Array;
> 

RM 3.3.1(8): The _subtype_indication_ or full type definition of an 
_object_declaration_ defines the nominal subtype of the object. The 
_object_declaration_ declares an object of the type of the nominal subtype.

> AR1 : aliased Stream_Element_Array := ( 2, 4, 5 );

AR1 nominal subtype is Stream_Element_Array (<>) of type 
Stream_Element_Array (<>)

> AR2 : aliased Stream_Element_Array ( 1 .. 3 ) := ( 2, 4, 5 );

AR2 nominal subtype is Stream_Element_Array (1 .. 3) of type 
Stream_Element_Array (<>)

> 
> AR1A : Stream_Element_Array_access := AR1'access;
> 
> -- Illegal
> AR2A : Stream_Element_Array_access := AR2'access;
> 
> 
RM/TC1 3.10.2 (24): ... The view denoted by the prefix X shall satisfy 
the following additional requirements, presuming the expected type for 
the X'Access is the general access type A with designated type D:

RM/TC1 3.10.2 (27/1): ...; if D is untagged, then the type view shall be 
D, and A's designated subtype either statically match the nominal 
subtype of the view or be discriminanted and unconstrained.

A = Stream_Element_Array_Access
D = Stream_Element_Array (<>)

D - untagged; type of both view is Stream_Element_Array (<>) = D; and 
A's designated subtype (Stream_Element_Array (<>)) is discriminanted and 
unconstrained.


What's wrong?


Vadim Godunko