Ruby Hash.merge with specified keys only

I'm pretty sure I saw on a Rails related site something along the lines of:

def my_function(*opts)
  opts.require_keys(:first, :second, :third)
end

And if one of the keys in require_keys weren't specified, or if there were keys that weren开发者_如何学C't specified, an exception was raised. I've been looking through ActiveSupport and I guess I might be looking for something like the inverse of except.

I like to try and use as much of the framework as possible compared to writing my own code, that's the reason I'm asking when I know how to make the same functionality on my own. :)

At the moment I'm doing it through the normal merge routine and making sure that I have what I need with some IFs.

I think the method you're thinking of is assert_valid_keys (documentation here) but this only raises an exception if any unexpected keys exist in the hash, not if any of the specified keys are missing. i.e. if a hash is being used to pass options to a method it can be used to check for invalid options not for required options.

You can do this yourself relatively easily. As was stated in an earlier answer, half your work is done for you in assert_valid_keys. You can roll your own method to do the rest.

def my_function( *opts )
  opts.require_and_assert_keys( :first, :second, :third )
end

create lib/hash_extensions.rb with the following:

class Hash
  def require_and_assert_keys( *required_keys )
    assert_valid_keys( keys )
    missing_keys = required_keys.inject(missing=[]) do |missing, key|
      has_key?( key ) ? missing : missing.push( key )
    end
    raise( ArgumentError, "Missing key(s): #{missing_keys.join( ", ")}" ) unless missing_keys.empty?
  end
end

finally, in config/environment.rb, add this to make it work:

require 'hash_extensions'