code: func Wrap(c context.Context) context.Context {
  	if _, ok := c.(*cacheContext); ok {
  		return c
  	}
  	return &cacheContext{Context: c}
  }
docs: // Wrap wraps the supplied Context in a caching Context. All Value lookups will
  // be cached at this level, avoiding the expense of future Context traversals
  // for that same key.