square_brackets.rb

#################################################################################################
# This is probably the most tricky one -                                                        #
# {} is also syntax for blocks, but only when passed to a method OUTSIDE the arguments parens.  #
# When you invoke methods without parens, ruby looks at where you put the commas to figure out  #
# where the arguments end (where the parens would have been, had you typed them)                #
#################################################################################################

1.upto(2) { puts 'hello' } # it's a block
1.upto 2 { puts 'hello' } # syntax error, ruby can't figure out where the function args end
1.upto 2, { puts 'hello' } # the comma means "argument", so ruby sees it as a hash - th