docs: function BaseCache (opts) {
    this.opts = opts = opts || {}
    this.getCacheKey = opts.getKey || function () { return '_default' }
    this.getTags = opts.getTags || function () { return [] }
    this.getMaxAge = typeof opts.maxAge !== 'function' ? function () { return opts.maxAge } : opts.maxAge
  
    this.serialize = opts.serialize || function (v) { return v }
    this.deserialize = opts.deserialize || function (v) { return v }
  
    this.maxValidity = typeof opts.maxValidity === 'undefined'
      ? function () { return Infinity }
      : (typeof opts.maxValidity === 'function' ? opts.maxValidity : function () { return opts.maxValidity })
  }