Today we are going to see the basic differences between Block, Procs and Lambda. 

All these three are commonly used as inputs to some iterators like each and map.

• Blocks

Blocks can't be stored in a variable and are not considered as an object.

Blocks are simply few lines of codes that are used together as an input to another method.

A block is always invoked with the help of the yield statement as follows 

    > ["one","two","three"].each { |letter| print "#{letter.upcase} " }
    ONE TWO THREE  => ["one", "one", "three"]
    > ["one","two","three"].each do |letter|
    >    print "#{letter.upcase}"
    > end
    ONE TWO THREE  => ["one", "one", "three"]

• Procs

Procs and blocks almost same but the only difference between procs and blocks is that we can store proc in a variable which makes it useful for the future purpose.

We can also pass procs as arguments to functions.

And Procs can be used separately several times.

p = Proc.new { puts "Hello Tom" }
p.call  # prints 'Hello Tom'
p.class # returns 'Proc'
a = p   # a now equals p, a Proc instance
p       # returns a proc object '#<Proc:0x007f96b1a60eb0@(irb):46>'

•  Lambda

We can explicitly use return statement inside lambda because in this lambda it will only return from itself.

The number of arguments which have to be passed to lambda is counted so we can't pass the wrong number of arguments.

It is just like a regular function whose last statement is it's returned value as follows

lam = lambda { |x| puts x }    # creates a lambda that takes 1 argument
lam.call(2)                    # prints out 2
lam.call                       # ArgumentError: wrong number of arguments (0 for 1)
lam.call(1,2,3)                # ArgumentError: wrong number of arguments (3 for 1)

or one more example

def lambda_test
  lam = lambda { return }
  lam.call
  puts "Hello Tom"
end

lambda_test                 # calling lambda_test prints 'Hello Tom'

So hope this blog was helpful to understand blocks, procs and lambdas.