code: function extractionFunction(type) {
    if (utils.isObject(type)) {
      return type
    }
    else if (!fns.hasOwnProperty(type)) {
      throw new FieldError('Unknown DimExtractionFn type: ' + type) 
    }
  
    var args = utils.args(arguments, 1)
      , fn = {
        type: type
      }
  
    fns[type].apply(fn, args)
  
    return fn
  }
docs: Generate dimension extraction function object
  
  @see http://druid.io/docs/0.6.121/DimensionSpecs.html
  @see {extractionFunctions}
  @param {string|object} type Extraction function type
  @param {...*} arguments Extraction-specific arguments
  @returns {object} Best extraction function object ever