mezzanine/src/to-fast-props.js

Fantasy land union types with pattern matching

//@flow
'use strict'

let fastProto = null

// Creates an object with permanently fast properties in V8. See Toon Verwaest's
// post https://medium.com/@tverwaes/setting-up-prototypes-in-v8-ec9c9491dfe2#5f62
// for more details. Use %HasFastProperties(object) and the Node flag
// --allow-natives-syntax to check whether an object has fast properties.
function FastObject(o) {
	// A prototype object will have "fast properties" enabled once it is checked
	// against the inline property cache of a function, e.g. fastProto.property:
	// https://github.com/v8/v8/blob/6.0.122/test/mjsunit/fast-prototype.js#L48-L63
  //$FlowIssue
  if (fastProto !== null && typeof fastProto.property) {
    const result = fastProto
    fastProto = FastObject.prototype = null
    return result
  }
  fastProto = FastObject.prototype =
    o == null
      ? Object.create(null)
      : o
  return new FastObject
}

// Initialize the inline property cache of FastObject.
FastObject()

function toFastproperties<T: Object>(o: T) {
  return FastObject(o)
}

export default toFastproperties