Ruby optional parameters

Question

If I define a Ruby functions like this:

def ldap_get ( base_dn, filter, scope=LDAP::LDAP_SCOPE_SUBTREE, attrs=nil )

How can I call it supplying only the first 2 and the last args? Why isn't something like

ldap_get( base_dn, filter, , X)

possible or if it is possible, how can it be done?

Thanks for any replies!

Answer 1

It isn't possible to do it the way you've defined ldap_get. However, if you define ldap_get like this:

def ldap_get ( base_dn, filter, attrs=nil, scope=LDAP::LDAP_SCOPE_SUBTREE )

Now you can:

ldap_get( base_dn, filter, X )

But now you have problem that you can't call it with the first two args and the last arg (the same problem as before but now the last arg is different).

The rationale for this is simple: Every argument in Ruby isn't required to have a default value, so you can't call it the way you've specified. In your case, for example, the first two arguments don't have default values.

Answer 2

This isn't possible with ruby currently. You can't pass 'empty' attributes to methods. The closest you can get it to pass nil:

ldap_get(base_dn, filter, nil, X)

However, this will set the scope to nil, not LDAP::LDAP_SCOPE_SUBTREE.

What you can do is set the default value within your method:

def ldap_get(base_dn, filter, scope = nil, attrs = nil)
  scope ||= LDAP::LDAP_SCOPE_SUBTREE
  ... do something ...
end

Now if you call the method as above, the behaviour will be as you expect.

Answer 3

You are almost always better off using an options hash.

def ldap_get(base_dn, filter, options = {})
  options[:scope] ||= LDAP::LDAP_SCOPE_SUBTREE
  ...
end

ldap_get(base_dn, filter, :attrs => X)