How to chain calls in a pl/sql object type of functions returning SELF

You cannot both change the object and assign to it at the same time. You already know the solution, "build a new rectangle with SELF". But it won't be a lot of work.

Replace this:

  MEMBER FUNCTION setWidth(w NUMBER) RETURN rectangle IS    BEGIN        stWidth(w);        RETURN SELF;  END;

with this:

  MEMBER FUNCTION setWidth(w NUMBER) RETURN rectangle IS      v_rectangle rectangle := self;    BEGIN        v_rectangle.width := w;        RETURN v_rectangle;  END;

You were actually getting a compilation error. By default, SELF is an IN parameter. The call to stWidth failed because it was modifying an IN parameter with self.width := w;.

See: http://docs.oracle.com/cd/B28359_01/appdev.111/b28371/adobjbas.htm#CHDCFEEE

SELF is always the first parameter passed to the method.

• In member functions, if SELF is not declared, its parameter mode defaults to IN.

• In member procedures, if SELF is not declared, its parameter mode defaults to IN OUT. The default behavior does not include the NOCOPY compiler hint.

Sorry, I am a bit late, but the other answers are incorrect, at least using Oracle 11gR2, and what you are trying to achieve is entirely possible indeed.

I just have recently stumbled upon the problem and I see one can definitively return a reference to SELF exactly as you were trying to, without yielding to any trade-off or applying workarounds.

The only thing one needs is to redefine the method by (explicitly) setting the (implicit) SELF parameter as SELF IN OUT rectangle.
The SELF is the leading parameter that is silently passed to every object method, and for functions is defined as IN (immutable; this is what presumably makes the compiler complain). This is sort of established at compile time, but the good part is that when invoking the method you can omit it.
In the example at the end of the post (slightly rewritten from yours), we define a

MEMBER FUNCTION incrementWidth(SELF IN OUT rectangle, w NUMBER) RETURN rectangle

and we execute it omitting the SELF reference:

declare  r rectangle := rectangle(1,2);begin  dbms_output.put_line('width is: ' || r.width);  dbms_output.put_line('new width is: ' || r.incrementWidth(3).width);end;/

Note that there are two warnings to be aware of.

warning 1

Every method call will temporarily create a fresh copy of the object.
But just temporarily, the new instance is short lived, just between the start and the end of the method.This is inherent to using IN OUT parameters on all functions or procedures, and is not specific to object types. If you want to prevent this behaviour, you may want to redefine the signature of your function using the NOCOPY hint:

MEMBER FUNCTION incrementWidth(SELF IN OUT NOCOPY rectangle, w NUMBER) RETURN rectangle

See ORACLE-BASE - NOCOPY for more details. Note it is a hint however, that doesn't assure you are finally using the same object reference and not a newly created object, so use with caution.

warning 2

Given you have raised this question, chances are that you have a OOP background, and you may get a surprise when trying to invoke the method without using the returned reference like this

r.incrementWidth(10);

The compiler will return an error:

PLS-00221: 'INCREMENTWIDTH' is not a procedure or is undefined

So what is happening here? Well, the so called "static polymorfism" (i.e. the selection of the method overload during compilation) in pl/sql is slightly different than in other OOP languages, because it takes into account even the usage of the RETURNed type. To solve this, add a companion procedure with a signature whose difference is just in the lack of a returned type:

MEMBER FUNCTION incrementWidth(SELF IN OUT rectangle, w NUMBER) RETURN rectangle,MEMBER PROCEDURE incrementWidth(SELF IN OUT rectangle, w NUMBER)

Reasonably, if you don't want to duplicate the same code in the function and the procedure, the procedure will internally delegate the function; and depending on the version of Oracle you are using you may want to play with code inlining (see OCP: More New PL/SQL Features) to achieve the same speed as a copy-pasted implementation (hardly you'll notice a real difference). Explicit "inlining" points at a method by name, however it works also in this case where the method name is overloaded.

In the example below you will see that either the function or procedure is alternatively invoked depending on the usage of the returned/not_returned parameter.

so finally...

The code one may want to write is the following (I have not used the NOCOPY not to pollute the relevant stuff, but it is straightforward to do)

CREATE OR REPLACE TYPE rectangle AS OBJECT(  length NUMBER,  width NUMBER,  CONSTRUCTOR FUNCTION rectangle(length NUMBER, width NUMBER)    RETURN SELF AS RESULT,  MEMBER FUNCTION incrementWidth(SELF IN OUT rectangle, w NUMBER) RETURN rectangle,  MEMBER PROCEDURE incrementWidth(SELF IN OUT rectangle, w NUMBER));/CREATE OR REPLACE TYPE BODY rectangle AS  CONSTRUCTOR FUNCTION rectangle(length NUMBER, width NUMBER)    RETURN SELF AS RESULT  AS  BEGIN    SELF.length := length;    SELF.width := width;    RETURN;  END;  MEMBER FUNCTION incrementWidth(SELF IN OUT rectangle, w NUMBER) RETURN rectangle IS    BEGIN        dbms_output.put_line('...invoking the function with input ' || w);        width := width + w;        RETURN SELF;  END;  MEMBER PROCEDURE incrementWidth(SELF IN OUT rectangle, w NUMBER) IS    BEGIN        PRAGMA INLINE (incrementWidth, 'YES');        dbms_output.put_line('...invoking the procedure with input ' || w || ', that in turn is...');        self := incrementWidth(w);  END;END;/

Upon execution of...

set serveroutput onselect * from v$version where rownum = 1;declare  r rectangle := rectangle(1,2);begin  dbms_output.put_line('width is: ' || r.width);  --this is invoking the "function" version, because we are making use of  --the returned rectangle object  dbms_output.put_line('new width is: ' || r.incrementWidth(3).width);  --the original reference has been updated even without using the NO COPY hint  dbms_output.put_line('original object has width updated: ' || r.width);  --this is invoking the "procedure" version, because we are not using the returned object  r.incrementWidth(3);  --of course this has finally worked as well  dbms_output.put_line('again what is the new width like now?: ' || r.width);end;/

you get

BANNER                                                                     --------------------------------------------------------------------------------Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production  width is: 2...invoking the function with input 3new width is: 5original object has width updated: 5...invoking the procedure with input 3, that in turn is......invoking the function with input 3again what is the new width like now?: 8

You can't return SELF from a member function. You can create a copy, but I'm not sure why a setwidth function would return a rectangle object. I know this basic example probably came from some old Oracle docs, but I would not put a computed field (area) as an attribute. If its computed, it should be a member function (or procedure). Reason is that unless you want to always remember to update area in functions that affect area, you'll shoot yourself in the foot. Your example is broken (aside from the setWidth returning self), since only the constructor calculates area.

set serveroutput ondeclare  r rectangle := rectangle(3,2);begin  dbms_output.put_line('Area is: ' || r.area);  -- change the width  r.stWidth(4);  dbms_output.put_line('Area is: ' || r.area);end;

Output:

Area is: 6Area is: 6

Obviously this is incorrect. I would do something like:

CREATE OR REPLACE TYPE rectangle AS OBJECT(-- The type has 2 attributes.  len NUMBER,  width NUMBER,-- Define a constructor that has only 2 parameters.  CONSTRUCTOR FUNCTION rectangle(len NUMBER, width NUMBER)    RETURN SELF AS RESULT,  MEMBER PROCEDURE setLength(l NUMBER),  MEMBER PROCEDURE setWidth(w NUMBER),  MEMBER FUNCTION getArea return NUMBER,  MEMBER PROCEDURE showArea);CREATE OR REPLACE TYPE BODY rectangle AS  CONSTRUCTOR FUNCTION rectangle(len NUMBER, width NUMBER)    RETURN SELF AS RESULT  AS  BEGIN    SELF.len := len;    SELF.width := width;    RETURN;  END;  MEMBER PROCEDURE setLength(l NUMBER) IS  BEGIN    self.len := l;  END;  MEMBER PROCEDURE setWidth(w NUMBER) IS  BEGIN    self.width := w;  END;  MEMBER FUNCTION getArea return NUMBER IS  BEGIN    return self.len * self.width;  END;  MEMBER PROCEDURE showArea IS  BEGIN    -- Just shows how we calculated area and spits to console    dbms_output.put_line('Area is: ' || self.getArea || ' (' || self.len || ' * ' || self.width || ')');  END;END;

And this way you'd have:

set serveroutput ondeclare  r rectangle := rectangle(3,2);begin  dbms_output.put_line('Area is: ' || r.getArea);  -- change the width  r.setWidth(4);  dbms_output.put_line('Area is: ' || r.getArea);end;

Output:

Area is: 6Area is: 12