No named parameters in Ruby?

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What’s actually happening:

# Assign a value of "meh" to scope, which is OUTSIDE meth and equivalent to
#   scope = "meth"
#   meth(1, scope)
meth(1, scope = "meh")

# Ruby takes the return value of assignment to scope, which is "meh"
# If you were to run `puts scope` at this point you would get "meh"
meth(1, "meh")

# id = 1, options = "meh", scope = "scope"
puts options

# => "meh"

There is no support* for named parameters (see below for 2.0 update). What you’re seeing is just the result of assigning "meh" to scope being passed as the options value in meth. The value of that assignment, of course, is "meh".

There are several ways of doing it:

def meth(id, opts = {})
  # Method 1
  options = opts[:options] || "options"
  scope   = opts[:scope]   || "scope"

  # Method 2
  opts = { :options => "options", :scope => "scope" }.merge(opts)

  # Method 3, for setting instance variables
  opts.each do |key, value|
    instance_variable_set "@#{key}", value
    # or, if you have setter methods
    send "#{key}=", value
  end
  @options ||= "options"
  @scope   ||= "scope"
end

# Then you can call it with either of these:
meth 1, :scope => "meh"
meth 1, scope: "meh"

And so on. They’re all workarounds, though, for the lack of named parameters.

Edit (February 15, 2013):

* Well, at least until the upcoming Ruby 2.0, which supports keyword arguments! As of this writing it’s on release candidate 2, the last before the official release. Although you’ll need to know the methods above to work with 1.8.7, 1.9.3, etc., those able to work with newer versions now have the following option:

def meth(id, options: "options", scope: "scope")
  puts options
end

meth 1, scope: "meh"
# => "options"

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