[Largo]

This PR continues the #89 item "Range#% and #step without a block". While working on it I found a broader cause: instance-variable writes on Ruby subclasses of built-in classes were always taking the slow path.

Changes

1. Instance-variable writes for subclasses of built-in classes

An instance of a Ruby subclass of Array, Hash, Enumerator and the like is an IRubyObject but not a RubyObject. An @x = v on such an object always took the slow, uncached path. This was true both in RubyOps.SetInstanceVariable/WriteInstanceVariable and in the method JIT's SetIVar.

These objects now take the cached store as well (RubyOps.TrySetRubyObjectInstanceVariable):

• The frozen flag is read from the object itself (IRubyObjectState), as RubyContext.IsObjectFrozen does.
• A String still takes the slow path, because that path also warns about chilled string literals.
• Exception subclasses keep their instance data elsewhere, so this PR does not change them.

2. ArithmeticSequence without Enumerator#initialize

Enumerator::ArithmeticSequence set its generator by calling Enumerator#initialize(nil) { }, a Ruby method with *args, &block. It now sets the three variables that call would have set directly.

Numbers

Release, net8.0:

	master	this PR	CRuby
AO.new.set (Array subclass, 4 ivar writes)	416 ns	267 ns	—
HO.new.set (Hash subclass, 4 ivar writes)	510 ns	307 ns	—
Enumerator subclass, 4 ivar writes	953 ns	694 ns	—
ArithmeticSequence.__build__	938 ns	510 ns	—
(1..100).step(3)	1505 ns	1102 ns	206 ns
(1..100) % 3	1804 ns	1363 ns	210 ns

For comparison, a plain object with 4 ivar writes takes ~90 ns. Most of what step still costs is its *args, &block signature and the sequence object itself.

Testing

• Frozen and edge cases: a script compares IronRuby with CRuby for these cases, and the output is identical:
  • writes on subclasses of Array, Hash, String and Enumerator after the JIT has specialized the methods;
  • frozen receivers (FrozenError);
  • dup and clone;
  • more than 20 variables.
• ArithmeticSequence: the existing step/inspect comparison is unchanged, and next, peek, with_index, each_slice, lazy, size, zip and rewind match CRuby.
• IronRuby.Tests: passes, with no failures.
• ruby/spec with no failures: language, core/kernel, core/hash, core/enumerator, core/range, core/exception, core/struct, core/basicobject.
• ruby/spec with known errors: core/array and core/string show the same known failures and errors as master.

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Generated by Claude Code

Summary by CodeRabbit

• Bug Fixes
  • Improved instance-variable assignment for supported Ruby objects, including objects outside the standard RubyObject type.
  • Updated arithmetic sequence initialization while preserving its generator behavior.

[coderabbitai]

Walkthrough

Instance-variable write paths now try a cached store for eligible Ruby objects. Arithmetic sequence initialization now assigns its generator Proc directly and marks the sequence initialized.

Changes: Cached instance-variable writes

Layer / File(s)	Summary
Ruby-object cached write path Src/Ruby/Runtime/RubyOps.cs, Src/Ruby/Runtime/Jit/JitRuntime.cs	SetInstanceVariable, WriteInstanceVariable, and JitRuntime.SetIVar try the cached write path for eligible Ruby objects. The existing fallback paths remain. The helper rejects frozen objects and MutableString instances.

Arithmetic sequence initialization

Layer / File(s)	Summary
Direct generator initialization Src/StdLib/ironruby/ruby4.rb	__arith_init__ assigns the generator Proc directly and sets @__initialized__ instead of calling initialize(nil) with a block.

Estimated code review effort: 2 (Simple) | ~12 minutes

Possibly related issues

• Largo/ironruby#89: The change directly initializes the ArithmeticSequence used by Range#step without a block. The summary does not establish a performance change.

Possibly related PRs

• Largo/ironruby#98: This PR adds cached writes for IRubyInstanceDataOwner and changes the cached-store interface. This change uses that interface for IRubyObject subclasses.

Suggested reviewers: sholden

Merge Risk: Minimal · up to 5f64e

The change caches eligible writes and directly initializes arithmetic sequences. No material merge-blocking risk was established.

Pre-merge checks: 4 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documenta…	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks: 4 passed

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title identifies cached instance-variable writes and the ArithmeticSequence initialization change.
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

Full details: Docstring Coverage

Explanation

Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documentation-only edits and deletions within surviving functions are included; unchanged diff context and fully deleted functions are excluded. Analyzed 4 functions across 3 files.

Resolution

Write docstrings for the functions missing them to satisfy the coverage threshold.

Finishing Touches

Generate docstrings

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Generate unit tests (beta)

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• Autofix · Keep fixing CodeRabbit findings and required CI, and resolving merge conflicts

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Brakeman (8.1.0)

Brakeman reported 52 analysis error(s); security analysis is incomplete

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Failed pre-merge checks:
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Write docstrings for the functions missing them to satisfy the coverage
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Commits

Reviewing files that changed from the base of the PR and between e682abb and 5f64e63.

Files selected for processing: 3

• Src/Ruby/Runtime/Jit/JitRuntime.cs
• Src/Ruby/Runtime/RubyOps.cs
• Src/StdLib/ironruby/ruby4.rb

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