如何向* args添加哈希？

Question

How do I conditionally add a hash to an *args array in Rails? I don't want to stomp on the original value if one exists.

For instance, I have an method that receives an array:

def foo(*args)
  # I want to insert {style: 'bar'} into args but only if !style.present?
  bar(*args)                              # do some other stuff 
end

I've started using the extract_options and reverse_merge methods provided by rails:

def foo(*args)
  options = args.extract_options!         # remove the option hashes
  options.reverse_merge!  {style: 'bar'}  # modify them
  args << options                         # put them back into the array
  bar(*args)                              # do some other stuff 
end

It works but seems verbose and not very ruby-ish. I feel like I've missed something.

Answer 1

Yes, #extract_options! is the way to do it in Rails. If you want to be more elegant, you'll have to alias it, or find your own way of handling this need, or search for gem by someone who has already done it.

Answer 2

A bit late to the party - but in case you need to do this on a regular basis it's worth using a little utility method for this - eg like the following, which merges an options -hash into an args -ary - and takes care of merging it with possibly existing hash-args or just appending it as new hash, if no hash is present in the args :

def merge_into_args!(opts={}, *args)
  opts.each do |key, val|
    if args.any?{|a| a.is_a?(Hash)}
      args.each{|a| a.merge!(key => val) if a.is_a?(Hash)}
    else
      args << {key => val}
    end
  end

  args
end

This comes in handy if you want to merge a modified options -hash back into *args and pass these along to another method, eg:

 # extract options from args
 options = args.extract_options!

 # modify options
 # ...
 # ...

 # merge modified options back into args and use them as args in another_method
 args = merge_into_args!(options,*args)
 another_method(*args)

 # or as 1-liner directly in the method call:
 another_method(*merge_into_args!(options,*args))

 # and in your case you can conditionally modify the options-hash and merge it 
 # back into the args in one go like this:
 another_method(*merge_into_args!(options.reverse_merge(style: 'bar'),*args))

Some more examples:

# args without hash 
args = ["first", "second"]

# merge appends hash
args = merge_into_args!({ foo: "bar", uk: "zok" },*args)
#=> ["first", "second", {:foo=>"bar", :uk=>"zok"}]

# Another merge appends the new options to the already existing hash:   
args = merge_into_args!({ ramba: "zamba", halli: "galli" },*args)
#=> ["first", "second", {:foo=>"bar", :uk=>"zok", :ramba=>"zamba", :halli=>"galli"}]

# Existing options are updated accordingly when the provided hash contains
# identical keys:
args = merge_into_args!({ foo: "baz", uk: "ZOK!", ramba: "ZAMBA" },*args)
#=> ["first", "second", {:foo=>"baz", :uk=>"ZOK!", :ramba=>"ZAMBA", :halli=>"galli"}]