Uso práctico de closures

Argumentos-bloque de código, list comprehensions, lambdas en Ruby, Python, Smalltalk

http://www.martinfowler.com/bliki/CollectionClosureMethod.html
http://www.martinfowler.com/bliki/Closure.html

The next most common closure method I use with collections is collect. This is similar but where you need to gather the results of a method call. Here's the traditional code:

  offices = []
for e in employees
offices <<>
Again the closure method allows you to use a one-liner.
offices = employees.collect {|e| e.office}
You can see what this does, it's similar to select but instead  puts the result of the method call into the returned  collection. Smalltalk also called this 'collect'. Lisp has a similar  function called 'map', in ruby 'map' is an alias for 'collect'. 
There's a concept that's come out of modern functional programming languages that's similar to the two preceding closure methods - it's called a list comprehension. List comprehensions have made  their way into the python language. They provide a syntactic approach to getting the kinds of benefits we've seen so far. Here are the two examples again using python list comprehensions.
  managers = [e for e in employees if e.isManager]
offices = [e.office for e in employees]
List comprehensions make it easy to combine the two.
managersOffices = [e.office for e in employees if e.isManager]
  total = 0
for e in employees
 total += e.salary
end
Inject does it like this.
total = employees.inject(0) {|result, e| result + e.salary}
At each element in the collection inject assigns the result of  executing the block to the result variable. The result of the final  execution gets returned from inject.