The following is an example of the Iterator usage in Ruby.

The following is an example of the Iterator usage in Ruby.

Iterator
Definition

A Ruby iterator is simple a method that can invoke a block of code.

• The Block is generally followed by the method, and the code in the block may not necessarily be executed.
• If the method contains yield, the Code in its block will be executed.
• The Block can receive parameters and return values.

def two_times  yield  yieldendtwo_times { puts "Hello" }# Hello# Hellodef fib_up_to(max) i1, i2 = 1. 1 while i1 <= max   yield i1   i1, i2 = i2, i1 + i2 endendfib_up_to(1000) { |f| print f, " " }# 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987

The i1 after yield in the above Code will be passed into the block as parameter and assigned to the argument f of the block.
The Block can contain multiple arguments.

Common iterator
Each

Each is probable the simplest iterator-all it does is yield successive elements of its collection.

[1, 3, 5, 7, 9].each { |i| puts i }# 1 # 3# 5# 7# 9

Find

A blocl may also return a value to the method. The value of the last expression evaluated in the block is passed back to the method as the value of the yield.

class Array def find  each do |value|    return value if yield(value)  end endend[1,3,4,7,9].find { |v| V*V > 30 } # => 7

Collect (also known as map)

Which takes each element from the collection and passes it to the block. The results returned by the block are used to construct a new array

["H", "A", "L"].collect { |x| x.succ } # => ["I", "B", "M"]

Inject

The inject method lets you accumulate a value within ss the members of a collection.

[1,3,5,7].inject { |sum, element| sum + element } # => 16# sum = 1, element = 3# sum = 4, element = 5# sum = 9, element = 7# sum = 16[1,3,5,6].inject { |product, element| product*element } # => 105

If inject is called with no parameter, it uses the first element of the collections as the initial value and starts the iteration with the second value.

Another simple method of writing the above Code:

[1,3,5,7].inject(:+) # => 16[1,3,5,7]/inject(:*) # => 105

Interaction between Iterator and I/O Systems

Iterators can not only access data in Array and Hash, but also interact with I/O systems.

f = File.open("testfile")f.each do |line| puts "The line is: #{line}"endf.close

Produces:
The line is: This is line one
The line is: This is line two
The line is: This is line three