Add opt-in ClrArrayConversion.LiveView interop mode for CLR arrays#2721
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Options.Interop.ClrArrayConversion selects how CLR arrays cross into script: Copy (default, per-conversion JsArray snapshot, behavior unchanged) or LiveView, which exposes single-rank T[] as a fixed-size ArrayWrapper<T> live view routed through the same WrapObjectHandler and identity-cache machinery as other wrapped CLR objects. - element reads/writes go straight to the underlying array in both directions; script writes are coerced to the element type - resize attempts (push/pop/shift/unshift/splice, length writes, out-of-bounds index writes) throw a JS TypeError instead of leaking CLR exceptions; delete mirrors integer-indexed exotic semantics (false in range, true out of range) so pop/shift cannot zero slots - Array.isArray stays false; iteration, spread, attached Array.prototype methods and JSON.stringify-as-array work like other array-like wrappers - multi-rank (T[,]) and non-zero-based (T[*]) arrays keep Copy-mode behavior under both modes Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Flip the default of Options.Interop.ArrayConversion from Copy to LiveView so single-rank CLR arrays (T[]) cross into script as live, fixed-size wrapper views instead of per-read deep-copied JsArray snapshots -- aligning T[] with wrapped List<T> and cutting ~2.9x time / ~75% allocation on array-member traversal. Copy stays available to preserve the pre-4.14 behavior. Also rename the option (added in the unreleased sebastienros#2721) from ClrArrayConversion to ArrayConversion, enum ArrayConversionMode: Interop already implies CLR, and Copy/LiveView are exclusive modes (like StepMode), not a combinable ...Type flags enum. Migrate the tests that specifically exercised Copy-snapshot semantics (array identity cache, sebastienros#2541 element writability) and four extension-method tests to pin Copy explicitly: a CLR method returning T[] now yields a wrapper that AsArray() rejects, and the LINQ .join() case additionally resolves the Enumerable.Join extension method on the wrapper's IEnumerable<T> target instead of falling back to native Array.prototype.join (PreferJsPrototypeMethods mitigates). Refresh the interop churn benchmark comments/config for the new default. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
lahma
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Jul 21, 2026
Flip the default of Options.Interop.ArrayConversion from Copy to LiveView so single-rank CLR arrays (T[]) cross into script as live, fixed-size wrapper views instead of per-read deep-copied JsArray snapshots -- aligning T[] with wrapped List<T> and cutting ~2.9x time / ~75% allocation on array-member traversal. Copy stays available to preserve the pre-4.14 behavior. Also rename the option (added in the unreleased #2721) from ClrArrayConversion to ArrayConversion, enum ArrayConversionMode: Interop already implies CLR, and Copy/LiveView are exclusive modes (like StepMode), not a combinable ...Type flags enum. Migrate the tests that specifically exercised Copy-snapshot semantics (array identity cache, #2541 element writability) and four extension-method tests to pin Copy explicitly: a CLR method returning T[] now yields a wrapper that AsArray() rejects, and the LINQ .join() case additionally resolves the Enumerable.Join extension method on the wrapper's IEnumerable<T> target instead of falling back to native Array.prototype.join (PreferJsPrototypeMethods mitigates). Refresh the interop churn benchmark comments/config for the new default. Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This was referenced Jul 22, 2026
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Part of the V8-gap performance campaign (#1775 follow-up); completes the array-interop story started in #2716.
Change
New
Options.Interop.ClrArrayConversionenum:Copy(default — exact current behavior, locked by tests) andLiveView. UnderLiveView, a single-rankT[]crossing into script becomes a live, fixed-sizeArrayWrapper<T>view — aligned with how wrappedList<T>already behaves — instead of a per-read deep-copiedJsArraysnapshot:push, growth, length write) throws a JSTypeError— never a leaking CLRNotSupportedException.Array.isArrayisfalse(matches the other wrappers; documented);for..of, spread andArray.prototypemethods work via the attached array prototype;JSON.stringifystill serializes as an array.T[,]) and non-zero-based arrays keep their existing behavior in both modes._typeMappersmemoization.Numbers (default BDN job,
InteropWrapperChurnBenchmark.ArrayMemberTraversal: 100 reads of anint[100]member per op)LiveView needs no identity flag for its 2.5× / −75% alloc win (live semantics, fresh wrapper per crossing); combined with an identity flag, array reads hit the wrapper cache like any other host object. Memory-probe verified: zero retained growth after full GC over 200k iterations.
Gates
Rebased on current main (includes #2716–#2720): Jint.Tests 3689/3626 (net10/net472, includes 31 new LiveView tests), PublicInterface 114/114 both TFMs (API-approval snapshot updated for the new enum/property), Test262 99,431 passed / 0 failed.
InteropTests.NonWritableArrayElement_*andShouldConvertArrayToArrayInstancepass unchanged under defaultCopy.A follow-up proposal issue for flipping the default to
LiveViewin the next major (aligningT[]withList<T>semantics) will be filed once this merges.🤖 Generated with Claude Code