PROPOSAL: Return 'this' (original) (raw)
Marek Kozieł develop4lasu at gmail.com
Wed Mar 25 14:59:06 PDT 2009
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AUTHOR: Lasu aka Marek Kozieł
OVERVIEW
FEATURE SUMMARY: It allows the method to return reference to 'this' object.
MAJOR ADVANTAGE: Simplification of “return this” statement. 'void' can be easy replaced with 'this'.
MAJOR BENEFIT(s): It would prevent NullPointerException, and make some 'builder' like interfaces look really clear and simple.
MAJOR DISADVANTAGE: Returned value cannot be changed while inheritance, also other objects cannot be returned.
ALTERNATIVES: Self-bounded generics, This type, change returned type for every method on each inheritance.
EXAMPLES
SIMPLE/ADVANCED EXAMPLE: public class Builder {
String text = "";
public this add (char c){text+=c;}
public this add (String c){ if (c==null){ text +="null"; return; // this will be returned } text+=c; }
public static void test(Builder builder) { builder.add('.').add("test()").add(':'); }
}
package test;
public class ReturnThis {
static class A { public this test() { } }
static class B extends A { }
static Class getReturnedType(Class classs) { try { return classs.getMethod("test").getReturnType(); } catch (SecurityException e) { e.printStackTrace(); } catch (NoSuchMethodException e) { e.printStackTrace(); } return null; }
public static void main(String[] args) { System.out.println(getReturnedType(A.class)); // will print: class returnThis.ReturnThis$A
System.out.println(getReturnedType((new A()).getClass()));
// will print: class returnThis.ReturnThis$A
System.out.println(getReturnedType(B.class));
// will print: class returnThis.ReturnThis$B
System.out.println(getReturnedType((new B()).getClass()));
// will print: class returnThis.ReturnThis$B} }
DETAILS
SPECIFICATION: JLS 8.4 (modifications)
ResultType: Type void this*
A method declaration either specifies the type of value that the method returns, uses the keyword void to indicate that the method does not return a value, or uses the keyword this to indicate that the method return the reference to 'this' object.
*Keyword this for return cannot occurs if method is static.
JLS 14.17 (modifications)
ReturnStatement: return Expressionopt ;
A return statement with no Expression must be contained in the body of a method that is declared, using the keyword void, not to return any value (§8.4), or in the body of a method that is declared, using the keyword this , to return this reference (§8...),or in the body of a constructor (§8.8).
COMPILATION: Method just before exiting from it's scope returns 'this'. Exceptions work same as before. Returned object type is actual object type.
TESTING: Normal way.
LIBRARY SUPPORT: No.
REFLECTIVE APIS: No.
OTHER CHANGES: None.
MIGRATION: None.
COMPATIBILITY Backward: full. Forward: Only jars.
http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6479372
http://java.net/cs/user/view/cs_msg/37432
http://lasu2string.blogspot.com/2009/03/return-this-proposal.html
PS. Maybe this Joe consider as 'proposal'. Any questions?
-- Pozdrowionka. / Regards. Lasu aka Marek Kozieł
http://lasu2string.blogspot.com/
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