Question

I face a weirb problem with optionals parameters in ruby.
This is my code :

def foo options={:test => true}
    puts options[:test]
end

foo # => puts true
foo :lol => 42 # => puts nil

I can not figure out why the second call puts nil.
Is seems that putting an other parameter set :test to nil.

Thanks.

Answer 1

It happens because if it is a default parameter, passing a hash parameter will completely overwrite it (ie. it sets options = {:lol => 42}), so the options[:test] key no longer exists.

To give particular hash keys default values, try:

def foo options={}
  options = {:test => true}.merge options
  puts options[:test]
end

In this case, we merge a hash with default values for certain keys ({:test => true}), with another hash (containing the key=>values in the argument). If a key occurs in both hash objects, the value in the hash passed to the merge function will take precedence.