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Array's hole should be undefined rather than 0 #323
Description
What happened
See below example
What you expected
It should match js behavior
Minimal reproduction
const values = new Array(4);
console.log("values.length", values.length);
console.log("values[1]", values[1]);
console.log("values[1] === undefined", values[1] === undefined);
console.log("1 in values", 1 in values);
console.log("Object.keys(values)", Object.keys(values));
const read = values[1];
console.log("read !== undefined", read !== undefined);
values[2] = undefined;
console.log("values[2]", values[2]);
console.log("values[2] === undefined", values[2] === undefined);
console.log("2 in values", 2 in values);Command you ran:
perry test.ts && ./testOutput:
values.length 4
values[1] 0
values[1] === undefined false
1 in values false
Object.keys(values) []
read !== undefined true
values[2] undefined
values[2] === undefined true
2 in values false
Expected:
values.length 4
values[1] undefined
values[1] === undefined true
1 in values false
Object.keys(values) []
read !== undefined false
values[2] undefined
values[2] === undefined true
2 in values true
Environment
- Perry version: -/5/408
- Host OS: ArchLinux
- Target: native
- Rust toolchain (if building from source): rustc 1.95.0 (59807616e 2026-04-14)
- Installed via: from source
Diagnostic output
Perry Doctor
Environment Checks
──────────────────
✓ perry version: 0.5.408
✓ update status: up to date
✓ clang (LLVM codegen): clang version 22.1.3
✓ system linker (cc): cc (GCC) 15.2.1 20260209
✓ runtime library: /home/codehz/Projects/perry/target/release/libperry_runtime.a
⚠ project config (perry.toml): not found - run: perry init
All critical checks passed with some warnings.
Anything else
Also found in my ecs's demo
Activity
[-]Array cannot have hole in perry[/-][+]Array's hole should be undefined rather than 0[/+]proggeramlug commentedon Apr 30, 2026
Fixed in 2f04bb1 (v0.5.412). Your literal repro now matches Node byte-for-byte:
Implementation uses an internal
TAG_HOLEsentinel for never-written slots soObject.keys/incan distinguish a hole from an explicitarr[i] = undefinedwrite, while reads translate HOLE → UNDEFINED so user code never sees the sentinel. Pinned viatest-files/test_issue_323_array_holes.ts— exercises your repro shape plus theMIN_ARRAY_CAPACITY=16padding boundary, the empty-array edge, and a function-scoped for-loop hitting the bounded-index inline fast path.fix(runtime): sparse-array gap-fill uses TAG_HOLE not 0.0 (v0.5.738)
fix(object): Object.keys/values/entries on a string no longer SIGSEGV (…