Here are methods that store and retrieve … something, probably. The author had to make up method names because map[string]interface{} doesn't have an interface we could satisfy.

  func (ctx *Context) SetObject(object interface{}, key string) { … }
  func (ctx *Context) Object(key string) interface{} { … }

Here a caller has to provide a method that takes an arbitrary number of … whatever.

  type rowScanner interface {
  	Scan(...interface{}) error
  }