Mutating arguments - clarifications from written test.

mutating_arguments.rb

# From LaunchSchool written test 2017-07-07

def shout(string)
  string + "!!!"   # => "hello world!!!"  # Just an operation, not a method on `string`. Silimar to `1 + 1`. Argument `string` stays coupled to `sentence`
  string.upcase!   # => "HELLO WORLD"     # Mutates the caller
end                # => :shout

sentence = "hello world"  # => "hello world"
shout(sentence)           # => "HELLO WORLD"

puts sentence  # => nil

###########################

def shout(string)
  string += "!!!"  # => "hello world!!!" # Non-mutating method, shorthand for `string = string + '!!!'`. Saves to new memory address & decouples `string` from `sentence`. `
  string.upcase!   # => "HELLO WORLD!!!" # Already decoupled (above), so `string` does not affect `sentence`
end                # => :shout

sentence = "hello world"  # => "hello world"
shout(sentence)           # => "HELLO WORLD!!!"

puts sentence  # => nil

############################

def shout(string)
  string << "!!!"  # => "hello world!!!" # Mutates the caller (argument `string` stays coupled to `sentence`)
  string.upcase!   # => "HELLO WORLD!!!" # Mutates the caller again (argument `string` stays coupled to `sentence`)
end                # => :shout

sentence = "hello world"  # => "hello world"
shout(sentence)           # => "HELLO WORLD!!!"

puts sentence  # => nil

# >> HELLO WORLD
# >> hello world
# >> HELLO WORLD!!!