PROPOSAL: Glue classes based on Extension Methods (original) (raw)

Marek Kozieł develop4lasu at gmail.com
Mon Mar 30 23:27:46 PDT 2009

GENESIS I simplified glue classes and described it basing on Extension Methods, but it still can be extended to support static / static methods "ArrayList..create();" and static variables. The main difference rely on the way glue method is executed (almost no names conflicts). I hope that this version will be easier to understood, especially the way TypeParameters are split.

AUTHOR: Lasu aka Marek Kozieł

OVERVIEW

FEATURE SUMMARY: Glue classes allow to execute static methods on objects using double dot notation.

MAJOR ADVANTAGE: Simplification of localizing additional functionality

MAJOR BENEFIT(s):

MAJOR DISADVANTAGE:

ALTERNATIVES: Utils classes, more work on project, duplicated code...

EXAMPLES SIMPLE / ADVANCED EXAMPLE: See below.

DETAILS SPECIFICATION:

Extension Methods:

public class Extensions{ public static int countWords(this String str){ return str.Split(...)...; }

public static String[] split(this String str, boolean trim){
    return str.Split(...)...;
}

}

To make it Glue class we extract type linked with 'this' to class header, remove parameter name occurring after 'this', remove static word, and use 'this' as simple parameter:

public class base glue (String ){ public int countWords(this){ return this.split(...)...; }

public String[] split(this, boolean trim){
    return this.split(...)...;
}

}

How do we execute methods:

Extension Methods: int count = “Extension Methods”.countWords();

Glue classes: base is in import and no other glue method exists with same name for this object: int count = “Extension Methods”..countWords();

or base is in import: int count = “Extension Methods”..base.countWords();

or int count = “Extension Methods”..com.some.base.countWords();

GENERICS:

Extension Methods: public class Extensions{ public static T getLast(this ArrayList list){ return list.get(list.size()-1); }

    public static <T> T getFirstValid(this ArrayList<T> list,

Validator<? super T> validator){ for (T t : list){ if (validator.isValid(t)) return t; } return null; }

}

Glue classes: public class base glue ( ArrayList ){ public T getLast( this ){ return list.get(list.size()-1); }

    public T getFirstValid( this , Validator<? super T> validator){
        for (T t : list){
            if (validator.isValid(t)) return t;
        }
        return null;
    }

}

How do we execute methods (glue): void test(ArrayList list){ System.out.print(“Last:” + list..getLast() ); }

Advanced: public class base glue ( ArrayList ){

    public <S> T getFirstValid( this , Validator<? super T,S>

validator, S condition){ for (T t : list){ if (validator.isValid( t, condition )) return t; } return null; }

}

Execution: void test(ArrayList list, Condition condition){ System.out.print(“First:” + list..getFirstValid(Condition.validator, condition ) ); }

Notice that T cannot be directly specified while it's always determined by object used as 'this'

COMPILATION All methods are compiled to simple static form (like this visible in extension methods:) , so they can be executed in normal way. The extracted method header (like: glue (ArrayList)) to class header is used for grouping methods properly. Method: $glue (ArrayList nothing){}; is created basing on: “ glue (ArrayList)” and used for matching control and determining which class is glue type.

TESTING: Like simple static methods.

LIBRARY SUPPORT: No.

REFLECTIVE APIS: No.

OTHER CHANGES: No.

MIGRATION: None.

COMPATIBILITY New jars are fully compatible. Code is only backward compatible.

REFERENCES: http://msdn.microsoft.com/en-us/library/bb383977.aspx

http://bugs.sun.com/view_bug.do?bug_id=4093687

http://mail.openjdk.java.net/pipermail/coin-dev/2009-March/000680.html

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