Hash argument of Ruby

gistfile1.rb

require 'json'

def print_json(data)
  puts JSON.dump(data)
end

print_json(1) #=> 1
print_json([1]) #=> [1]
print_json({a:1}) #=> {"a":1}
print_json({a:1, b: 2}) #=> {"a":1,"b":2}

print_json 1 #=> 1
print_json [1] #=> [1]
#print_json {a: 1} #=> syntax error
#print_json {a: 1, b: 2} #=> syntax error
print_json a: 1 #=> {"a":1}
print_json a: 1, b: 2 #=> {"a":1,"b":2}


# why?
print_json [1] #=> OK
print_json({a: 1}) #=> OK
#print_json {a: 1} #=> NG
print_json a: 1 #=> OK