From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me X-Spam-Level: X-Spam-Status: No, score=-1.3 required=5.0 tests=BAYES_00,INVALID_MSGID autolearn=no autolearn_force=no version=3.4.4 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: 103376,fbbb6c094bab8a9d X-Google-Attributes: gid103376,public From: nasser@apldbio.com (Nasser Abbasi) Subject: Re: Help (gnat 3.04) Date: 1996/06/14 Message-ID: #1/1 X-Deja-AN: 160071261 sender: news@biosys.apldbio.COM references: to: cktan@kelly.teleport.com (Chong-Kwan Tan) organization: Applied BioSystems newsgroups: comp.lang.ada Date: 1996-06-14T00:00:00+00:00 List-Id: From: cktan@kelly.teleport.com (Chong-Kwan Tan) Hi, I am trying to link all items in an array into a list and gnat 3.04 gives me this error: % gnatmake tt.adb gcc -c tt.adb tt.adb:21:37: object has deeper accessibility level than access type gnatmake: "tt.adb" compilation error Could someone tell me why? Thanks, -tan ==================================================================== 1 procedure TT is 2 3 type Item_Type; 4 type Item_Ptr_Type is access all Item_Type; 5 type Item_Type is 6 record 7 Next : Item_Ptr_Type; 8 end record; 9 type Item_Table_Type is 10 array (Positive range <>) of aliased Item_Type; 11 12 type Pool_Type is 13 record 14 Item : Item_Table_Type(1..10); 15 end record; 16 17 procedure Init 18 (Pool : in out Pool_Type) is 19 begin 20 for I in 2 .. Pool.Item'Last loop 21 Pool.Item(I-1).Next := Pool.Item(I)'Access; 22 end loop; 23 Pool.Item(Pool.Item'Last).Next := null; 24 end Init; 25 26 P : Pool_Type; 27 begin 28 Init(P); 29 end TT; -- You are passing P as In OUT, this seems to be the cause of the problem. the only think I could think of is that at line 21, the right hand side is an access to the local copy of pool.item(I) that is passed as "IN", so this copy of the P object sits on the call frame of procedure Init, i.e. it is a local copy of P that Init is processing, and so, the program is trying to take the address of a local object and assign it to a object whose dynamic life is longer (the right hand side), since pool is also passed in as OUT parameter, which refers to object outside the procedure Init, and so you get the error. i.e. Inside Init, when doing pool.item(I)'access, this is getting the address of the IN copy of P. So, I guess this means one can not pass in an object as IN OUT if one intends to gets its address ? it is the only thinh that would explain to me as it seems on the surface the access type life time rules are obeyed... Any way, to Init pool , just call Init with pool as OUT only and that will work, since this way the adress that is being taken belong to an object that lives as long as what is being assigned to, which is itself, so Ada is happy, end every one is happy, and life is good. procedure T is type Item_Type; type Item_Ptr_Type is access all Item_Type; type Item_Type is record Next : Item_Ptr_Type; end record; type Item_Table_Type is array (Positive range <>) of aliased Item_Type; type Pool_Type is record Item : Item_Table_Type(1..10); end record; P : Pool_Type; Procedure Init_ver2 (Pool: out Pool_Type) is begin for I in 2 .. P.Item'Last loop P.Item(I-1).Next := P.Item(I)'Access; end loop; P.Item(P.Item'Last).Next := null; end Init_ver2; begin Init_Ver2(P); end T; -- Nasser Abbasi. C/C++/Ada Solaris. GeneAssist - A client/server application for Nucleic acid and protein sequence search and analysis. PE-Applied BioSystem division. email: nasser@apldbio.com MSEE, MSCS, MSCE, FM (and Karpov is my chess hero! ..).