Implement empty record / list optimisations.

src/list.js

@@ -77,29 +77,41 @@ class TypeInferedList extends BaseImmutableList {
  const Type = this.constructor
 
  if (input === null || input === void(0)) {
- if (!Type[$empty]) {
+ if (!this[$empty]) {
  const result = construct(this)
  result[$store] = ImmutableList()
  result.size = 0
- Type[$empty] = result
+ this[$empty] = result
  }
 
- return Type[$empty]
+ return this[$empty]
  }
 
- if (input instanceof Type && input.constructor === Type) {
+ if (input instanceof Type && input && input.constructor === Type) {
  return input
  }
 
-
- const list = this[$init]()
  const source = Indexed(input)
+ const isEmpty = source.size === 0
+
+ if (isEmpty && this[$empty]) {
+ return this[$empty]
+ }
+
+
+ let list = this[$init]()
  list.size = source.size
  source.forEach((value, index) => {
  list.set(index, value)
  })
 
- return this[$result](list)
+ list = this[$result](list)
+
+ if (isEmpty) {
+ this[$empty] = list
+ }
+
+ return list
  }
  [Typed.step](result, [key, value]) {
  return change(result, (store=ImmutableList()) => store.set(key, value))

src/record.js

@@ -41,19 +41,27 @@ class TypedRecord extends IterableKeyedBase {
  return result.asImmutable()
  }
 
- [Typed.read](structure={}) {
+ [Typed.read](structure) {
  const Type = this.constructor
 
- if (structure instanceof Type && structure.constructor === Type) {
+ if (structure instanceof Type &&
+ structure &&
+ structure.constructor === Type) {
  return structure
  }
 
- if (!structure || typeof(structure) !== "object") {
+ if (structure === null || (structure && typeof(structure) !== "object")) {
  return TypeError(`Invalid data structure "${structure}" was passed to ${this[$typeName]()}`)
  }
 
  const seq = Seq(structure)
  const type = this[$type]
+ const isEmpty = seq.size === 0
+
+
+ if (isEmpty && this[$empty]) {
+ return this[$empty]
+ }
 
  let record
  for (let key in type) {
@@ -68,7 +76,13 @@ class TypedRecord extends IterableKeyedBase {
  record = this[$step](record || this[$init](), [key, result])
  }
 
- return this[$result](record)
+ record = this[$result](record)
+
+ if (isEmpty) {
+ this[$empty] = record
+ }
+
+ return record
  }
  [Typed.step](result, [key, value]) {
  const store = result[$store] ? result[$store].set(key, value) :
@@ -118,9 +132,8 @@ class TypedRecord extends IterableKeyedBase {
  return this
  }
 
- const RecordType = this.constructor
  return this[$empty] ||
- (RecordType[$empty] = new RecordType())
+ (this[$empty] = new this.constructor())
  }
 
  remove(key) {