PROPOSAL: 'final' without explicit type (update) (original) (raw)
Marek Kozieł develop4lasu at gmail.com
Mon Mar 30 14:26:16 PDT 2009
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AUTHOR: Lasu aka Marek Kozieł
OVERVIEW
FEATURE SUMMARY:
MAJOR ADVANTAGE: It allows people to concentrate on logic during operating on heavy generics and to use values which are more intuitive for them than variables.
MAJOR BENEFIT(s):
- It allows to avoid duplicating unnecessarily types of declaration.
- It increase a concentration on 'what I've got' than on 'what type is that' (we decrease size by one to obtain last element index, not because we can do this = it's int), while for variables we still keep concentrate on: 'what type is that' / 'what I can put there'.
- Editing existing code to get some value from method chain is easier.
- That method can be itself multi-thread with this, but it's a far future.
- Using of Generics is easier.
MAJOR DISADVANTAGE: Certainly, some people will overuse this solution. Consider operator is easier to read. It might be a problem if a person does not know how to give proper names for values.
ALTERNATIVES: Normal variables.
EXAMPLES
SIMPLE / ADVANCED EXAMPLE: public Map<String,ArrayList> readMaping(){ final map = new HashMap<String,ArrayList>(); for( final row : readLine() ){ String key = row.get(0); row.remove(0); map.put(key, row); } return map; }
public Map<String,ArrayList> readMaping(){ final map; //compile time error map= new HashMap<String,ArrayList>(); for( final row : readLine() ){ String key = row.get(0); row.remove(0); map.put(key, row); } return map; }
public class Final { static final maping = new HashMap<String, ArrayList>(); }
public class Final { static final maping = (Map<String,ArrayList>)loadMap(); }
DETAILS
SPECIFICATION: FieldDeclaration FieldDeclaration would be extended to allow omitting Type declaration if field is final and it's directly followed by assignment of new class instance creation(created object type would be used), or by Anonymous Constructors (JLS 15.9.5.1 )(direct superclass S would be used), or Enum constants preceded by EnumType (JLS 8.9) (Enum type would be used), or CastExpression (JLS 15.16) (ReferenceType would be used).
SPECIFICATION: LocalVariableDeclarationStatement (JLS 14.4) Local Variable Declaration Statements would be extended to allow omitting Type declaration if field is final and listed rules taking place:
- VariableInitializer appears.
- Variable is not initialized directly with null (this can be discussed).
- VariableInitializer type is neither primitive nor Object. --> primitive : they should not be mixed with Object-s to easy. --> Object : when object type is Object, we mostly deal with situation 'Unknown type', so this should not be hidden.
- If VariableInitializer - Expression type is intersection type (we always omit Object type in intersection), then: --> If intersected types have common ancestor then this ancestor is used as type. --> If effect of intersected types is one Interface, then this interface is used as type. --> In other way, an error occurs.
COMPILATION: Just as today, value type only need to be determined.
TESTING: The same as final-s variables.
LIBRARY SUPPORT: No.
REFLECTIVE APIS: No.
OTHER CHANGES: No.
MIGRATION: None.
COMPATIBILITY Only code is no forward compatible.
REFERENCES RFE: Add Immutable types to Java: http://bugs.sun.com/view_bug.do?bug_id=4459053
Typedef (alias): http://bugs.sun.com/view_bug.do?bug_id=4983159
http://lasu2string.blogspot.com/2009/03/final-without-explicit-type-proposal.html
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