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Ruby on Rails® for Microsoft Developers by Antonio Cangiano

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4.3. Looping

The Ruby language offers two categories of looping statements: "built-in loops" and iterators. Ruby has three types of built-in loops: for, while, and until. A few differences aside, these are constructs that you should already be accustomed to from other languages.

Ruby also offers an infinite loop construct, through the loop method.

Despite being employed at times, idiomatic Ruby code tends to favor iterators that can also be customized to reflect the needs of your code.

4.3.1. The for/in Loop

The for statement in Ruby iterates over a collection of elements. To be more exact, it enables you to iterate through enumerable objects such as arrays, hashes, and ranges. This is its basic syntax:

for element in collection
  # Do something with element
  code
end

Notice that the statement requires both the for and in keywords, and as such it acts similarly to the For Each in Visual Basic, and foreach in C#, not their simple For and for versions.

These are a few examples that use for to loop through collections:

# Prints the integers between 0 and 10
for i in 0..10
  puts i
end

# Prints each element of the array
for el in [2, 4, 6, 8, 10]
  puts el
end

# Prints each key-value pair in the hash
h = { :x => 24, :y => 25, :z =>26 }
for key, value in h
  puts "#{key} => #{value}"
end

Similarly to if, unless, and case, for is terminated by end, and it accepts an optional separator token. Only, instead of being then, do is the keyword as shown here:

for c in 'a'..'z' do
  puts c
end

This ...

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