StdLib Map Set

Map, Set, WeakMap, WeakSet

Collection types for storing key-value pairs and unique values.

Implementation Status: 100% Complete

Overview

Type	Methods	Implemented
Map	13	13
Set	18	18
WeakMap	5	5
WeakSet	4	4
Total	40	40

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Map

A collection of key-value pairs with any key type.

Static Methods

Method	Status	Description
Map.groupBy(items, callback)	Implemented	Groups by callback key (ES2024)
Map[Symbol.species]	Implemented	Returns constructor

Prototype Methods

Method	Status	Description
set(key, value)	Implemented	Adds/updates entry, returns Map
get(key)	Implemented	Returns value or undefined
has(key)	Implemented	Checks if key exists
delete(key)	Implemented	Removes entry, returns boolean
clear()	Implemented	Removes all entries
forEach(callback, thisArg)	Implemented	Iterates entries
entries()	Implemented	Returns [key, value] iterator
keys()	Implemented	Returns key iterator
values()	Implemented	Returns value iterator
size (getter)	Implemented	Returns entry count
[Symbol.iterator]	Implemented	Alias for entries()

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Set

A collection of unique values.

Static Methods

Method	Status	Description
Set[Symbol.species]	Implemented	Returns constructor

Prototype Methods

Method	Status	Description
add(value)	Implemented	Adds value, returns Set
has(value)	Implemented	Checks if value exists
delete(value)	Implemented	Removes value, returns boolean
clear()	Implemented	Removes all values
forEach(callback, thisArg)	Implemented	Iterates values
entries()	Implemented	Returns [value, value] iterator
keys()	Implemented	Alias for values()
values()	Implemented	Returns value iterator
size (getter)	Implemented	Returns value count
[Symbol.iterator]	Implemented	Alias for values()

Set Methods (ES2025)

Method	Status	Description
union(other)	Implemented	Returns new Set combining both
intersection(other)	Implemented	Returns common elements
difference(other)	Implemented	Returns elements not in other
symmetricDifference(other)	Implemented	Returns exclusive elements
isSubsetOf(other)	Implemented	Checks if all elements in other
isSupersetOf(other)	Implemented	Checks if contains all of other
isDisjointFrom(other)	Implemented	Checks for no common elements

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WeakMap

A Map with weakly held object keys (allows garbage collection).

Prototype Methods

Method	Status	Description
set(key, value)	Implemented	Key must be object
get(key)	Implemented	Returns value or undefined
has(key)	Implemented	Checks if key exists
delete(key)	Implemented	Removes entry

Limitations

• Keys must be objects (no primitives)
• Not iterable (no forEach, entries, etc.)
• No size property
• Entries auto-removed when key is garbage collected

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WeakSet

A Set with weakly held object values.

Prototype Methods

Method	Status	Description
add(value)	Implemented	Value must be object
has(value)	Implemented	Checks if value exists
delete(value)	Implemented	Removes value

Limitations

• Values must be objects (no primitives)
• Not iterable
• No size property
• Values auto-removed when garbage collected

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Key Differences

Feature	Map/Set	WeakMap/WeakSet
Key/Value Types	Any	Objects only
Enumerable	Yes	No
size property	Yes	No
Prevents GC	Yes	No
Use Case	General storage	Metadata on objects

Implementation Notes

SameValueZero

Map and Set use SameValueZero for key/value comparison:

• NaN === NaN is true
• +0 === -0 is true

Insertion Order

Map and Set maintain insertion order during iteration.

Weak Reference Implementation

WeakMap and WeakSet use .NET's ConditionalWeakTable internally.

Files

File	Purpose
StdLib/MapSet/MapConstructor.cs	Map constructor
StdLib/MapSet/MapPrototype.cs	Map prototype
StdLib/MapSet/SetConstructor.cs	Set constructor
StdLib/MapSet/SetPrototype.cs	Set prototype
StdLib/MapSet/WeakMapConstructor.cs	WeakMap constructor
StdLib/MapSet/WeakMapPrototype.cs	WeakMap prototype
StdLib/MapSet/WeakSetConstructor.cs	WeakSet constructor
StdLib/MapSet/WeakSetPrototype.cs	WeakSet prototype
JsTypes/JsMap.cs	Map implementation
JsTypes/JsSet.cs	Set implementation
JsTypes/JsWeakMap.cs	WeakMap implementation
JsTypes/JsWeakSet.cs	WeakSet implementation

See Also

• WeakCollections - Deep dive into weak references
• Iterator-Protocol - Collection iteration