Array's hole should be undefined rather than 0

[codehz]

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 && ./test

Output:

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

[proggeramlug]

Fixed in 2f04bb1 (v0.5.412). Your literal repro now matches Node byte-for-byte:

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

Implementation uses an internal TAG_HOLE sentinel for never-written slots so Object.keys / in can distinguish a hole from an explicit arr[i] = undefined write, while reads translate HOLE → UNDEFINED so user code never sees the sentinel. Pinned via test-files/test_issue_323_array_holes.ts — exercises your repro shape plus the MIN_ARRAY_CAPACITY=16 padding boundary, the empty-array edge, and a function-scoped for-loop hitting the bounded-index inline fast path.