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Added support for WeakMap and WeakSet - #21
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WeakMap and WeakSet were rejected as host-only names. They are now standard globals backed by host weak collections, with the spec surface and V8 messages. Any object is a valid key. A weak collection cannot enter a run, and leaves it as undefined, like an iterator.
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🟡 Changes recommended
WeakMap object-entry handling must match JavaScript semantics, and the new wrapper types must be added to the documented value model.
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What changed in this PR
Adds sandbox support for WeakMap and WeakSet, including JavaScript-like constructors and methods, weak-key validation, boundary handling, tests, parity coverage, and documentation.
Changes:
- Adds weak collection wrappers, built-ins, methods, globals, and dispatch registration.
- Prevents weak collections from crossing unsupported host boundaries.
- Adds escape, boundary, parity, and documentation coverage.
- Requires correction of
WeakMapiterable entry handling and completion of wrapper-model documentation.
| File | Description |
|---|---|
packages/maple/src/values/wrappers/wrapper.ts |
Adds weak collection wrappers to the wrapper model. |
packages/maple/src/values/wrappers/weak-set-wrapper.ts |
Defines the sandbox WeakSet wrapper. |
packages/maple/src/values/wrappers/weak-map-wrapper.ts |
Defines the sandbox WeakMap wrapper. |
packages/maple/src/support/can-be-held-weakly.ts |
Validates allowable weak collection keys and entries. |
packages/maple/src/host-functions.spec.ts |
Tests rejection of weak collections as host-function arguments. |
packages/maple/src/evaluator/language/references.ts |
Removes weak collection names from blocked globals. |
packages/maple/src/evaluator/host-bridge.ts |
Reports weak collections as unconvertible host arguments. |
packages/maple/src/escapes.spec.ts |
Tests prototype and constructor escape protections. |
packages/maple/src/builtins/weak-set/weak-set.ts |
Implements the WeakSet constructor and branding. |
packages/maple/src/builtins/weak-set/weak-set.spec.ts |
Covers WeakSet behavior and errors. |
packages/maple/src/builtins/weak-set/weak-set-prototype.ts |
Registers WeakSet methods. |
packages/maple/src/builtins/weak-set/methods/has.ts |
Implements WeakSet.has. |
packages/maple/src/builtins/weak-set/methods/delete.ts |
Implements WeakSet.delete. |
packages/maple/src/builtins/weak-set/methods/add.ts |
Implements WeakSet.add. |
packages/maple/src/builtins/weak-map/weak-map.ts |
Implements the WeakMap constructor and branding. |
packages/maple/src/builtins/weak-map/weak-map.spec.ts |
Covers WeakMap behavior and errors. |
packages/maple/src/builtins/weak-map/weak-map-prototype.ts |
Registers WeakMap methods. |
packages/maple/src/builtins/weak-map/methods/set.ts |
Implements WeakMap.set. |
packages/maple/src/builtins/weak-map/methods/has.ts |
Implements WeakMap.has. |
packages/maple/src/builtins/weak-map/methods/get.ts |
Implements WeakMap.get. |
packages/maple/src/builtins/weak-map/methods/delete.ts |
Implements WeakMap.delete. |
packages/maple/src/builtins/standard-globals.ts |
Exposes WeakMap and WeakSet globally. |
packages/maple/src/builtins/method-dispatch.ts |
Adds weak collection method dispatch. |
packages/maple/src/boundary/to-host.ts |
Drops or rejects weak collections during output conversion. |
packages/maple/src/boundary/to-host.spec.ts |
Tests weak collection output conversion. |
packages/maple/src/boundary/from-host.spec.ts |
Tests rejection of host weak collections as input. |
packages/maple/docs/language.md |
Documents supported constructors and globals. |
packages/maple/docs/builtins.md |
Documents the new weak collection APIs. |
packages/maple/docs/boundary.md |
Documents weak collection boundary behavior. |
packages/maple-parity/src/divergences.spec.ts |
Adds parity coverage for weak collections. |
packages/maple-parity/README.md |
Documents the interpreter parity divergence. |
Review effort: Lite
new Map(iterable) refused every entry that was not an array, and
read entry[0] and entry[1] off the host array directly. It now reads
both through the member model, as Object.fromEntries does, so
{ 0: key, 1: value } and Maple's own objects work as in JavaScript.
Merged
|
🎉 This PR is included in version 0.6.0 🎉 The release is available on: Your semantic-release bot 📦🚀 |
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What changes
Scripts can now use
WeakMapandWeakSet, for example to cache results per object or to track which objects a traversal has already visited. Before this change, reading either name threwDISALLOWED_SYNTAX.WeakMapsupportsget,set,hasanddelete.WeakSetsupportsadd,hasanddelete.Both behave as in JavaScript:
newinstanceofandString(...)give[object WeakMap]/[object WeakSet]new WeakMap(iterable)reads each entry likeentry[0]andentry[1], so{ 0: key, 1: value }works as a pairTypeError: Invalid value used as weak map key/Invalid value used in weak setget,hasanddeletewith a primitive returnundefined/falseinstead of throwingAny object can be a key, including functions and built-ins such as
Math. Scripts have no symbols, so nothing else can be.At the boundary, a weak collection's entries can't be listed, so it can't be copied:
dataor globals, or returned from a host function, it is rejected like any other unsupported value.undefined.TypeError: A WeakMap cannot be passed to the host.In all three cases it is handled the way an iterator is.
No new divergence from JavaScript. As with every built-in,
WeakMap.prototypeand.constructorstay blocked.The same entry reading fixes
new Map(iterable), which used to throw for every entry that was not an array:new Map([{ 0: 'a', 1: 1 }]).get('a')now gives1, as in JavaScript.How
WeakMapWrapperandWeakSetWrapperhold a real hostWeakMap/WeakSet, so entries keyed by throwaway objects can be garbage-collected during a long run. Scripts have noWeakReforFinalizationRegistry, so they can't observe when that happens. Neither wrapper has areadOnlyflag, because a weak collection can never arrive with frozen input.builtins/weak-map/andbuiltins/weak-set/follow the layout ofmap/andset/.support/can-be-held-weakly.tsdecides which values are valid keys.standard-globals.tsandmethod-dispatch.ts, and removed fromHOST_ONLY_NAMES.new WeakMapandnew Mapreadentry[0]andentry[1]throughgetMember, asObject.fromEntriesdoes. Any object works as a pair, and properties a script added to Maple's own objects are seen. Before this, theMapconstructor read the indexes off the host array directly.toHostdrops both wrappers. In strict mode, which is used for host-function arguments, it throwsUnconvertibleValueErrorinstead, andhost-bridge.tsreports that as aTypeErrorin the script.Tests, parity and docs
weak-map.spec.tsandweak-set.spec.tscover every method, the invalid-key messages, the constructor and its errors, and that set algebra refuses aWeakSet.map.spec.tsandweak-map.spec.tscover entries that are not arrays. Every expected value was checked against Node.escapes.spec.tschecks that.constructor,__proto__andWeakMap.prototypestay blocked.to-host.spec.ts,from-host.spec.tsandhost-functions.spec.tscover the boundary in both directions.Map,Set,WeakMaporWeakSet, and the parity package only covers scripts it can run.language.md(blocked names, thenewallowlist, theinstanceofcount, the wrappers in the value model), a new "WeakMap and WeakSet" section and the standard-globals list inbuiltins.md, and a new row in theboundary.mdtable.contact-summary.jsorcontact-ten-lines.js(measure-run, three alternating rounds).