Pure, Storage_Size and Unchecked_Conversion

["Y.Tomino" <demoonlit@panathenaia.halfmoon.jp>]

Hi.
I compiled the package like this with gcc 4.2.

with Ada.Unchecked_Conversion;
package Pure_SS_Unc is
   pragma Pure;
   type T is access Integer;
   for T'Storage_Size use 0;
   function F1 (X : Integer) return T;
   function F2 is new Ada.Unchecked_Conversion (Integer, T);
end Pure_SS_Unc;

Ada.Unchecked_Conversion is pure generic function.
I think the condition of F1 and F2 is the same.
but, I saw this message:

pure_ss_unc.ads:7:58: named access types not allowed in pure unit

   function F1 (X : Integer) return T; -- OK
   function F2 is new Ada.Unchecked_Conversion (Integer, T); -- NG

Why does compiler make an error at F2?

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