[Oberon] Protocols (interfaces) in Oberon-2
Jörg
joerg.straube at iaeth.ch
Tue Oct 27 16:01:55 CET 2020
Luca
I fully agree that with your proposed INTERFACE syntax the setup of the environment is much easier.
My proposed MODULE structure is more cumbersome to setup.
After you set up everything (implemented all needed interface procedures…), is there a big difference whether you write
in your syntax
NEW(i);
i.h := 3;
inc := i;
inc.IncBy2;
or in my syntax
New(i);
i.h := 3;
i.inc.IncBy2(i);
br
Joerg
Von: Oberon <oberon-bounces at lists.inf.ethz.ch> im Auftrag von Luca Boasso <luke.boasso at gmail.com>
Antworten an: ETH Oberon and related systems <oberon at lists.inf.ethz.ch>
Datum: Dienstag, 27. Oktober 2020 um 15:37
An: ETH Oberon and related systems <oberon at lists.inf.ethz.ch>
Betreff: Re: [Oberon] Protocols (interfaces) in Oberon-2
Although this is a solution to the problem, it doesn't buy you much because all generic signatures must have the type Data.Any.
To lift the limitation that the clients must know about the module Data we could extend Oberon-07 to support Component Pascal's ANYPTR type, defined as
ANYREC and ANYPTR
Each base record is implicitly regarded as an extension of the new abstract standard type ANYREC,
even if it is declared without explicit base type. ANYREC is an empty record that forms the root of all
record type hierarchies. ANYPTR is a new standard type that corresponds to a POINTER TO
ANYREC.
These new types make it easier to achieve interoperability between independently developed
frameworks, by allowing completely generic parameters.
The following pseudo definitions can be assumed:
ANYREC = ABSTRACT RECORD END;
ANYPTR = POINTER TO ANYREC;
PROCEDURE (a: ANYPTR) FINALIZE-, NEW, EMPTY;
But regardless, the beauty of interfaces is to be able to do something like the following:
MODULE Demo;
VAR W: Texts.Writer;
TYPE
I* = POINTER TO IDesc;
IDesc* = RECORD
h: INTEGER
END ;
R* = POINTER TO RDesc;
RDesc* = RECORD
h: REAL
END ;
Stringer* = INTERFACE
PROCEDURE ToString* (VAR a: ARRAY OF CHAR) ;
END ;
Incrementer* = INTERFACE
PROCEDURE IncBy2*();
END ;
PROCEDURE ( i : I ) ToString* (VAR a: ARRAY OF CHAR) ;
BEGIN a := "integer"
END ToString;
PROCEDURE ( r : R ) ToString* (VAR a: ARRAY OF CHAR) ;
BEGIN a := "real"
END ToString;
PROCEDURE ( i : I ) IncBy2*;
BEGIN i.h := i.h + 2
END IncBy2;
PROCEDURE ( r : R ) IncBy2*;
BEGIN r.h := r.h + 2.0
END IncBy2;
PROCEDURE CallStringer(s: Stringer);
VAR t: ARRAY 32 OF CHAR
BEGIN
s.ToString(t);
Texts.WriteString(W,t);
END CallStringer;
PROCEDURE Test*;
VAR i: I; r: R; ;
s: Stringer;
inc: Incrementer;
BEGIN
NEW(i); NEW(r);
i.h := 3;
r.h := 7.5;
(*
The assignment below allows for structural type compatibility between a
record (i) and an interface (s). Interfaces can only have PROCEDUREs in
their definition, if a record implements the set of PROCEDUREs of a
interface, it can then be assigned to it.
Any record implements the empty interface: INTERFACE END;
This is how the Go language works.
*)
inc := i;
inc.IncBy2;
inc := r;
inc.IncBy2;
CallStringer(i); (* this is an assignment to the formal parameter*)
CallStringer(r); (* this is an assignment to the formal parameter*)
(*
Alternatively we could still allow for nominal type compatibility
forcing the user to specify that a record implements a set of
interfaces:
I* = POINTER TO IDesc;
IDesc* = RECORD(Stringer, Incrementer)
h: INTEGER
END ;
The fact that a record implements an interface is explicit. This is
how Java does it. Extending from multiple interface types does not
bring the complexity and pitfalls of multiple inheritance.
To simplify the language in both cases, structural or nominal type
compatibility, we should drop the ability to extend RECORDs with other
records. Only INTERFACEs are allowed because we want only to extend
behavior not data. If you also need the data simply add compose
records as fields.
*)
END Test;
END Demo.
On Mon, Oct 26, 2020 at 2:29 PM Charles Perkins <chuck at kuracali.com> wrote:
Hmm...
Everything that implements an interface must be a descendant of Module Data but Data is empty, therefore its signature never needs to change. The use of an interface is checked in the CASE statement and cast there to the interface needed by the client. I think multiple interfaces can be implemented by successively extending Data. This could do it!
I am going to try to use this, thank you Jörg for your patience with me.
Cheers,
Chuck
On Mon, Oct 26, 2020 at 11:42 AM Jörg <joerg.straube at iaeth.ch> wrote:
Chuck
Okay. My proposal in standard Oberon-07 for your new requirement is this:
MODULE Data;
TYPE
Any* = POINTER TO Empty;
Empty* = RECORD END;
END Data.
MODULE Jsonify;
IMPORT Data;
TYPE
Methods* = POINTER TO MDesc;
MDesc* = RECORD
toJSON: PROCEDURE(this: Data.Any);
END;
END Jsonify.
MODULE myData;
IMPORT Data;
TYPE
Tree* = POINTER TO TreeDesc;
TreeDesc* = RECORD (Data.Empty)
left, right: Tree;
j: Jsonify;
END;
VAR t: Tree;
PROCEDURE J(t: Data.Any);
BEGIN
CASE t OF Tree: (* implement here your Tree-specific JSON routine *)
END
END J;
PROCEDURE New*(VAR t: Tree); BEGIN NEW(t); Jsonify.New(t.j); t.j.toJSON := J END New
BEGIN
New(t); t.j.toJSON(t)
END myData.
br
Jörg
Von: Oberon <oberon-bounces at lists.inf.ethz.ch> im Auftrag von Charles Perkins <chuck at kuracali.com>
Antworten an: ETH Oberon and related systems <oberon at lists.inf.ethz.ch>
Datum: Montag, 26. Oktober 2020 um 17:03
An: ETH Oberon and related systems <oberon at lists.inf.ethz.ch>
Betreff: Re: [Oberon] Protocols (interfaces) in Oberon-2
Hi Jörg and other interested people,
There is just one piece missing I think for the usage of Interfaces that I am looking for. I would like to be able to write a routine that doesn't know what Data is (in the provided example) but can still hold a pointer to it or to anything else that implements the JSONify interface (and not anything that doesn't implement the JSONify interface) and can call it's ToJSON procedure.
In my previous reply I incorrectly thought that a record in Oberon can be an extension of two base records, which is not right, and not what Jörg is presenting.
Apologies for my confusion,
Chuck
On Mon, Oct 26, 2020 at 7:37 AM Charles Perkins <chuck at kuracali.com> wrote:
Hi Jörg,
With this example I think I understand how Oberon can in fact already do what I want in composing Interfaces. In Wirthian fashion the mechanism is explicit rather than implicit. I had not made the mental jump to how a record may be based on more than one base record... with that, everything else falls into place.
I observe that this means that interfaces are 'opt in' rather than automatic based on just matching a subset of method names, but that's typical and arguably more safe anyway.
I'm going to think on this some more.
Thank you very much for taking the time to illustrate this to us.
Best,
Chuck
On Sun, Oct 25, 2020 at 11:55 PM Jörg <joerg.straube at iaeth.ch> wrote:
Chuck
> Andreas, in your scheme can you create separate protocols, for example
> "Jsonify" with the method ToJSON and a different protocol "Persistify" with
> the methods "Store" and "Load", and have other records implement one or the
> other or neither or both?
Here my proposal for doing this in standard Oberon-07.
In the previous mail, I separated interface/protocol and implementation for clarity. The same should be done here. For brevity, I combined the two here.
MODULE Data;
(* Definition of whatever your internal data structure looks like. Here just an example *)
TYPE
Tree* = POINTER TO TreeDesc;
TreeDesc* = RECORD val*: ARRAY 15 OF CHAR; left*, right*: Tree END
END Data.
MODULE Jsonify;
IMPORT Data;
TYPE
Methods* = POINTER TO MDesc;
MDesc* = RECORD
toJSON: PROCEDURE(this: Data.Tree);
END;
(* empty or default implementation *)
PROCEDURE J(this: Data.Tree); END J;
PROCEDURE New*(VAR m: Method); BEGIN NEW(m); m.toJSON := J END;
END Jsonify.
MODULE Persistify;
IMPORT Data;
TYPE
Methods* = POINTER TO MDesc;
MDesc* = RECORD
Load: PROCEDURE(VAR this: Data.Tree);
Store: PROCEDURE(this: Data.Tree)
END;
(* empty or default implementation *)
PROCEDURE L(VAR this: Data.Tree); BEGIN this := NIL END L;
PROCEDURE S(this: Data.Tree); END S;
PROCEDURE New*(VAR m: Methods); BEGIN NEW(m); m.Load := L; m.Store := S END Init;
END Persistify.
Here now a module using both interfaces/protocols and overwrite even one persist procedure with an own version, if wanted.
MODULE Usage;
IMPORT Data, Jsonify, Persistify;
TYPE
User = RECORD (Data.Tree)
j: Jsonify;
p: Persistify
END;
VAR u: User;
PROCEDURE myLoad(this: Data.Tree); (* implement your version of persist Load *) END myLoad;
PROCEDURE New*(VAR u: User);
BEGIN NEW(u); Jsonify.New(u.j); Persistify.New(u.p); u.p.Load := myLoad END New;
BEGIN
New(u); u.j.toJSON(u); u.p.Load(u) (* this calls my version *)
END Usage.
Adding the qualifiers "j" and "p" circumvents the ambiguity in case the two interfaces defined methods with the same name.
br
Jörg
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