CSC/ECE 517 Fall 2012/ch1 1w4 aj

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 algorithm syntax
• specialization or parameter currying
• parallel programming (e.g. the map-reduce problem)

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>

Continuation Passing Style

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

Topical References

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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.