Blocks (also referred to as closures, especially in other languages like JavaScript) are not a unique features of Ruby, but they're one that many people talk about (and more people use without realizing it!) What is a block?
A section of code which is grouped together.
Zzzzz....
A block is a piece of code that is not executed immediately. Instead, it is stored in a variable or passed to a method as a parameter to be potentially executed at a later time.
Sound complicated? Let's look at some Ruby.
[1,2,3,4].each do |number|
puts number * 100 # <= this is a block. :)
end
[1,2,3,4].each { |number|
puts number * 100 # <= this is a block too! :D
}number * 100 is a chunk of code, similar to what would be in a method, but in this case we don't need to go through all the trouble of creating a method just to iterate over some numbers.
Block can be identified by either do ... end or { }.
Block arguments are defined using a pair of | (pipe) characters. They look like a slide, so I like to say that we slide arguments into the block. For example:
[1,2,3].each do |number|
puts number # wheeeee! Right down the slide!
end
number is the block argument, this means that objects given to the block are going to be assigned to the number variable within the scope of the block. When the code in the block finishes execution, the block arguments are destroyed.