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== Introduction ==
 
 
=== Closures ===
 
====Code Blocks====
 
Before understanding the concept of Closures, let us take a brief introduction on “Code Blocks” in Ruby. A code block is a chunk of code, Ruby statements and expressions written between curly braces { } or between “do…end”.
For example:
 
<pre>
{  puts "Hello World!"  }
</pre>
 
or
 
<pre>
  do
    3.times(puts "Hello")
    object1.call
  end
</pre>
 
 
We can further segment generic algorithms down into the following examples:
 
* [[ #algos | basic algorithm syntax ]]
* [[ #curry | specialization or parameter currying ]]
* [[ #parallel | parallel programming (e.g. the map-reduce problem) ]]
 
==== <div id="algos">Basic Algorithms</div> ====
 
 
==== <div id="curry">Specialization / Currying Parameters</div> ====
 
[http://en.wikipedia.org/wiki/Currying Currying]
 
==== <div id="parallel">Parallel Programming - Map-Reduce</div> ====
 
The following Ruby thread example<ref>Flanagan, David and Yukihiro Matsumoto, The Ruby Programming Language. Sebastopol: O'Reilly Media, Inc., 2008. http://oreilly.com/catalog/9780596516178, pg 382</ref>
 
=== <div id="callbacks">Callbacks</div> ===
 
[http://en.wikipedia.org/wiki/Callback_(computer_programming) Callbacks] are often cited as the most desirable application of Closures<ref>"Learning more about Closures", StackOverflow.com. http://stackoverflow.com/questions/212401/javascript-how-do-i-learn-about-closures-usage</ref><ref>Morrison, Joe. "A Brief Introduction to Four Programming Language Concepts". http://joemorrison.org/projects/four-concepts/</ref>
 
Below are two important callback forms that can demonstrate this capability in common use.
 
* [[ #gui_handlers | GUI behavior injection ]]
* [[ #exceptions | generic exception handling ]]
 
==== <div id="gui_handlers">GUI behavior Injection</div> ====
 
 
==== <div id="exceptions">Generic Exception Handling</div> ====
 
=== <div id="management">Resource Management / Policy Enforcement</div> ===
 
==== <div id="resources">Maintaining Resources</div> ====
 
This often cited example shows the encapsulation of file base policy using a C++ and a Ruby Closure.<ref>Wikipedia Resource Acquisition is Initialization: http://en.wikipedia.org/wiki/Resource_Acquisition_Is_Initialization</ref>
 
==== <div id="policy">Resource Policy</div> ====
 
 
=== <div id="deferred">Deferred execution</div> ===
 
 
=== <div id="continuations">Continuation Passing Style</div> ===
 
<ref>Miller, Jeremy. "Functional Programming for Everyday .NET Development", MSDN Magazine. http://msdn.microsoft.com/en-us/magazine/ee309512.aspx</ref>.
 
=== <div id="syntax">Declarative syntax leads to less code</div> ===
 
== Topical References ==
 
<references/>
 
== Further Reading ==
 
[http://martinfowler.com/bliki/Closure.html Martin Fowler - Closure] : provides a basic definition of Closures and gives a few very basic examples.
 
[http://gafter.blogspot.com/2007/01/definition-of-closures.html Neal Gafter - A Definition of Closures] : gives a high-level, historical definition of Closures.
 
[http://onestepback.org/articles/invitationtoruby/reason4.html Jim Weirich - Top Ten Reasons I Like Ruby - Blocks and Closures] : provides several examples of how Closures can be useful in Ruby.
 
[http://www.skorks.com/2010/05/closures-a-simple-explanation-using-ruby/ Alan Skorkin - Closures - A Simple Explanation] : gives a high-level overview of Closures using Ruby examples.
 
[http://www.ibm.com/developerworks/java/library/j-cb01097/index.html IBM Developerworks - Crossing borders : Closures] : gives Ruby examples where Closures are useful.
 
[http://samdanielson.com/2007/9/6/an-introduction-to-closures-in-ruby Sam Danielson - An Introduction to Closures in Ruby] : high-level overview of using Closures in Ruby.
 
[http://csharpindepth.com/Articles/Chapter5/Closures.aspx C# in Depth - The Beauty of Closures] : demonstrates Closures in C#.
 
[http://en.wikipedia.org/wiki/Closure_(computer_science) Wikipedia - Closures] : everything there is to know about Closures on one page.
 
[http://ynniv.com/blog/2007/08/closures-in-python.html ynniv - Closures in Python] : examples implementing Closures in Python.
 
[http://msdn.microsoft.com/en-us/magazine/ee309512.aspx MSDN Magazine - Functional Programming .NET Development] : examples of functional style with Closures in C#.
 
[http://www.randomhacks.net/articles/2007/02/01/some-useful-closures-in-ruby Eric Kidd - Some useful closures, in Ruby] : demonstrates more examples of curried and specialized Closures in Ruby.
 
[http://weblog.raganwald.com/2007/01/closures-and-higher-order-functions.html Reg Braithwaite - Closures and Higher-Order Functions] : gives Ruby examples of specialized Closures.
 
[http://jibbering.com/faq/notes/closures Javascript Closures] : demonstrates Javascript Closures in callbacks.

Revision as of 20:46, 14 September 2012

Introduction

Closures

Code Blocks

Before understanding the concept of Closures, let us take a brief introduction on “Code Blocks” in Ruby. A code block is a chunk of code, Ruby statements and expressions written between curly braces { } or between “do…end”. For example: 

 {  puts "Hello World!"  }

or 

  do
     3.times(puts "Hello")
     object1.call
  end


We can further segment generic algorithms down into the following examples:

Basic Algorithms

Specialization / Currying Parameters

Currying

Parallel Programming - Map-Reduce

The following Ruby thread example<ref>Flanagan, David and Yukihiro Matsumoto, The Ruby Programming Language. Sebastopol: O'Reilly Media, Inc., 2008. http://oreilly.com/catalog/9780596516178, pg 382</ref>

Callbacks

Callbacks are often cited as the most desirable application of Closures<ref>"Learning more about Closures", StackOverflow.com. http://stackoverflow.com/questions/212401/javascript-how-do-i-learn-about-closures-usage</ref><ref>Morrison, Joe. "A Brief Introduction to Four Programming Language Concepts". http://joemorrison.org/projects/four-concepts/</ref>

Below are two important callback forms that can demonstrate this capability in common use.

GUI behavior Injection

Generic Exception Handling

Resource Management / Policy Enforcement

Maintaining Resources

This often cited example shows the encapsulation of file base policy using a C++ and a Ruby Closure.<ref>Wikipedia Resource Acquisition is Initialization: http://en.wikipedia.org/wiki/Resource_Acquisition_Is_Initialization</ref>

Resource Policy

Deferred execution

Continuation Passing Style

<ref>Miller, Jeremy. "Functional Programming for Everyday .NET Development", MSDN Magazine. http://msdn.microsoft.com/en-us/magazine/ee309512.aspx</ref>.

Declarative syntax leads to less code

Topical References

<references/>

Further Reading

Martin Fowler - Closure : provides a basic definition of Closures and gives a few very basic examples.

Neal Gafter - A Definition of Closures : gives a high-level, historical definition of Closures.

Jim Weirich - Top Ten Reasons I Like Ruby - Blocks and Closures : provides several examples of how Closures can be useful in Ruby.

Alan Skorkin - Closures - A Simple Explanation : gives a high-level overview of Closures using Ruby examples.

IBM Developerworks - Crossing borders : Closures : gives Ruby examples where Closures are useful.

Sam Danielson - An Introduction to Closures in Ruby : high-level overview of using Closures in Ruby.

C# in Depth - The Beauty of Closures : demonstrates Closures in C#.

Wikipedia - Closures : everything there is to know about Closures on one page.

ynniv - Closures in Python : examples implementing Closures in Python.

MSDN Magazine - Functional Programming .NET Development : examples of functional style with Closures in C#.

Eric Kidd - Some useful closures, in Ruby : demonstrates more examples of curried and specialized Closures in Ruby.

Reg Braithwaite - Closures and Higher-Order Functions : gives Ruby examples of specialized Closures.

Javascript Closures : demonstrates Javascript Closures in callbacks.

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