Defining and calling lambdas or procs (Ruby)

There are different ways to define a lambda or proc in ruby:

1. with lambda-keyword

   test = lambda do |arg|
     puts arg
   end
   

2. with the lambda literal -> (since ruby 1.9.1)

   test = -> (arg) do
     puts arg
   end
   

3. with the proc keyword (which defines a lambda that does not test the given number of arguments):

   test = lambda do |arg|
     puts arg
   end
   

And there are different ways to call them:

1. call (we prefer this)

   test.call('hello world')
   

2. Square brackets (could easily be mistaken for a hash)

   test['hello world']
   

3. .() (weird, isn't it?)

   test.('hello world')