Explain Iterator Syntax on Ruby on Rails

Question

I started learning Ruby on Rails and found myself confounded by the syntax, so I had to read about somet of the Ruby syntax. I learned the syntax from http://www.cs.auckland

Answer 1

What you see there is a block of code, the syntax is a bit awkward when you first see it.

So, basically, with iterators your have a "thing" that may be repeated, and it receives a block to know what to do.

For instance the Range class has a method called "each" which receives the block of code to execute on each element in the range.

Let's say you want to print it:

range = 1..10 #range literal 
range.each {|i|
    puts i
}

The code: {|i| puts i} is a block that says what to do when this range iterates over each one of its elements. The alternate syntax is the one you posted:

 range.each do |i|
      puts i 
 end

These blocks are used with iterators, but they are not limited to "iteration" code, you can use them in other scenarios, for instance:

class Person 
  def initialize( with_name ) 
    @name = with_name
  end
  # executes a block 
  def greet 
      yield @name #passes private attribute name to the block 
  end 
end 

p = Person.new "Oscar" 
p.greet { |n|
     puts "Name length = #{n.length}"
     puts "Hello, #{n}"
}

Prints:

Name length = 5
Hello, Oscar

So, instead of having a greet method with a fixed behavior, using block let the developer specify what to do, which is very helpful with iterators, but as you have just witness not the only place. In your case, that block is letting you specify what to do in the respond_to method.