respond_with

respond_with wraps a resource around a responder for default representation. First it invokes respond_to, if a response cannot be found (ie. no block for the request was given and template was not available), it instantiates an ActionController::Responder with the controller and resource.

Example

def index
  @users = User.all
  respond_with(@users)
end

It also accepts a block to be given. It’s used to overwrite a default response:

def destroy
  @user = User.find(params[:id])
  flash[:notice] = "User was successfully created." if @user.save

  respond_with(@user) do |format|
    format.html { render }
  end
end

All options given to respond_with are sent to the underlying responder, except for the option :responder itself. Since the responder interface is quite simple (it just needs to respond to call), you can even give a proc to it.