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From "Henri Yandell (JIRA)" <>
Subject [jira] Updated: (COLLECTIONS-233) Closure is an inaccurate name
Date Thu, 03 May 2007 19:43:15 GMT


Henri Yandell updated COLLECTIONS-233:

    Affects Version/s:     (was: Generics)
        Fix Version/s: Generics

Given that Java will be giving us Closures at some point in the future, it does seem that
the Generics version of Collections should consider changing the name. Switching 'Generics'
from affects version to fix version.

> Closure is an inaccurate name
> -----------------------------
>                 Key: COLLECTIONS-233
>                 URL:
>             Project: Commons Collections
>          Issue Type: Improvement
>          Components: Collection
>            Reporter: Stephen Kestle
>             Fix For: Generics
> The "Closure" in commons collections is not named well: for non-functional programmers
it will induce a "what's that?", and for functional programmers it will confuse expectations.

> From 
> A closure combines the code of a function with a special lexical environment bound to
that function (scope). 
> Java cannot pass functions, so the only way this can be done is with an (inner) class,
as follows (also from wikipedia): 
> class CalculationWindow extends JFrame { 
> private JButton btnSave; 
> ... 
> public final calculateInSeparateThread(final URI uri) { 
> // The expression "new Runnable() { ... }" is an anonymous class. 
> Runnable runner = new Runnable() { 
> void run() { 
> // It can access final local variables: 
> calculate(uri); 
> // It can access private fields of the enclosing class: 
> btnSave.setEnabled(true); 
> } 
> }; 
> new Thread(runner).start(); 
> } 
> } 
> Note how the Runnable accesses the btnSave variable in the function scope. This "special
lexical environment" is NOT the same as passing a parameter through a constructor OR execute
method. A Closure should NOT take a parameter for execute.  It is not actually possible to
have a "Closure" object, as that breaks the lexical environment.
> So, what to do? 
> I would propose an interface called Processor. It is more intuitive and has many "real
world" examples that can anchor the term so that it makes sense to the average programmer.

> For example, when applying for a passport, some documentation needs to be filled out,
and then it will go through a process to get you a passport. You hand (or send) your forms
to a clerk (Processor), and that's it. The Processor does not reply - the context that is
passed in your form (your details) allows a message to be sent back at a later date. 
> For backwards compatibility the interface would be  
>         public interface Processor<T> extends Closure<T>{} 
> with the appropriate documentation.   Closure would be deprecated with an appropriate
> However, it may be acceptable with the new version just to do a rename.

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