Return 'this' proposal (original) (raw)
Marek Kozieł develop4lasu at gmail.com
Sun Mar 15 14:34:27 PDT 2009
- Previous message: PRE-PROPOSAL: Source and Encoding keyword
- Next message: Return 'this' proposal
- Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]
AUTHOR: Lasu aka Marek Kozieł
GENESIS
It's a simplified 'This' type problem, which seems to be too much complicated as for now and need more analyses. Construction is designed not to interact with possibility that 'This' type will be introduced. OVERVIEW
FEATURE SUMMARY: It allows the method to return 'this' object.
MAJOR ADVANTAGE: Simplification of return this; statement. 'void' can be easy replaced with 'this'.
MAJOR BENEFIT(s):It would prevent NFP, in a described situation, and make some 'builder' like interfaces look really clear and simple.
MAJOR DISADVANTAGE: It's a change in language. Depending on the way that it would be compiled to byte-code, it determine compatibility(here may lie some problem that I do not know about).
ALTERNATIVES: Self-bounded generics.
EXAMPLES
SIMPLE/ADVANCED EXAMPLE: public class Builder {
public this add (char c){...}
public this add (String c){ if (c==null){ ... return; // this will be returned } ... }
public static void test(Builder builder) { builder.add('.').add("test()").add(':'); }
} DETAILS
SPECIFICATION: JLS 8.4: http://java.sun.com/docs/books/jls/third_edition/html/classes.html#8.4
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 called object.
Keyword this cannot occurs if method is static.
JLS 14.17: http://java.sun.com/docs/books/jls/third_edition/html/statements.html#14.17
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: Returned 'void' should be replaced with 'this', no more no less.
TESTING: Normal way.
LIBRARY SUPPORT: No.
REFLECTIVE APIS: No.
OTHER CHANGES:
I wander what object should represent 'this' return type in: Method.getReturnType(); (this.getObject() ?)
MIGRATION: None.
COMPATIBILITY Backward: full.
REFERENCES Bug: 6479372: http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6479372 http://java.net/cs/user/view/cs_msg/37432 Return 'this' proposal : http://lasu2string.blogspot.com/2009/03/return-this-proposal.html
-- Pozdrowionka. / Regards. Lasu aka Marek Kozieł
http://lasu2string.blogspot.com/
- Previous message: PRE-PROPOSAL: Source and Encoding keyword
- Next message: Return 'this' proposal
- Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]