Sample

Show that Zeitwerk::Loader#reload replaces every managed constant with a fresh Class object rather than updating the existing object in place, so pre-reload instances silently fail is_a? checks against the live constant after reload.

sha256:abab31760ab484a95ed188abe32ba188e2deb62bd52e9711ee179e047f362249

Case

Goal

Show that Zeitwerk::Loader#reload replaces every managed constant with a fresh Class object rather than updating the existing object in place, so pre-reload instances silently fail is_a? checks against the live constant after reload. HOW

Packages

zeitwerk 2.8.3

Environment

ruby

Created

2026-08-17T02:50:01Z

Commonly assumed

Calling loader.reload refreshes the source code for a constant while keeping the same Class object bound to that name, so existing instances continue to satisfy is_a?(Widget) and case/when Widget after reload.

The sample's author recorded this as what a developer or model would expect here. The contract below is what actually ran.

Contract

• After loader.reload, Widget is a different Class object than it was before reload — klass_before.equal?(klass_after) is false — meaning reload undefines the constant and installs a new autoload rather than patching the existing class in place.
• klass_before.name == 'Widget' && klass_after.name == 'Widget': both old and new objects report the same name string, so name-based inspection gives no indication that the identity changed.
• instance.is_a?(Widget) returns false for an instance created before reload, even though Widget.name is still 'Widget' and the instance's own class is still structurally identical.
• instance.is_a?(klass_before) returns true: the stale class object is still a valid Ruby Class; only its binding to the constant name has been removed.
• A case/when Widget branch does not match the pre-reload instance and routes it to the else branch with no exception raised — the mismatch is fully silent.

Files

• Gemfile
• Gemfile.lock
• NOTES.md
• app/widget.rb
• csx.json
• test/contract.rb

Download the verified artifact (tar.gz) — the exact bytes the contract ran against

Origin Seeder

csx-seed

Verification receipts

• ruby 3 · CONTAINER_RUN · compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS · rubygems@1 · 2026-08-17 · ed25519:d91480838ac982c9