Frozen empty base + non-mutating prepends#2
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memory_profiler on a heavy rijksakademie.nl page render showed this
gem allocating ~2.36 MB/request, with has_dom_attrs.rb:118
(DomStyle.new({})) alone accounting for 404 kB. Root cause: base
methods (dom_classes, dom_aria, dom_data, dom_style) always
allocate a fresh empty collection per call — components that
don't declare has_dom_* for that slot still pay the allocation,
and dom_attrs builds a 4-key hash + reject + deep_stringify +
deep_transform chain (4 hash allocations) on every call.
Changes:
* Base methods return shared frozen EMPTY_ARRAY / EMPTY_HASH /
EMPTY_STYLE constants. Zero allocation for components that
don't override.
* Prepends (has_dom_class, has_dom_aria, has_dom_data,
has_dom_style, has_dom_attr) switch from `super().tap { mutate }`
to `super() + [v]` / `super().merge(name => v)`. Required
because frozen bases can't be mutated; same allocation count
for components that DO override.
* DomStyle#merge preserves DomStyle type (so chained has_dom_style
declarations stay DomStyle all the way up).
* dom_attrs simplified to one `result = {}` + conditional key
assignments with localized `transform_keys` (skipping empty
slots), replacing the 4-allocation reduce chain. Behavior
preserved: output still stringifies + dasherizes top-level and
nested keys for aria/data.
Expected saving per render on a 400-component page:
~1.5–2 MB of allocation, ~100–150 ms of GC time. All 30 existing
assertions pass.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
tomasc
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Apr 18, 2026
The prepend defined by has_stimulus_* used `super().tap { |d| d[k] = ... }`
which mutates the hash returned by super. This works fine when
HasDomAttrs#dom_data returns a fresh mutable hash, but breaks when the
upstream base becomes a frozen shared constant (see tomasc/has_dom_attrs#2,
where EMPTY_HASH is returned to eliminate per-call allocations for
components that don't override).
Switching to `current.merge(k => v)` preserves behavior and works against
both the old mutable base and the new frozen base. No extra allocation in
the common case because the previous pattern also allocated a hash at the
bottom of the super chain.
All 71 existing assertions pass (1 pre-existing skip).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
2 tasks
tomasc
added a commit
to tomasc/has_stimulus_attrs
that referenced
this pull request
Apr 18, 2026
* Non-mutating prepend pattern for frozen-base compatibility
The prepend defined by has_stimulus_* used `super().tap { |d| d[k] = ... }`
which mutates the hash returned by super. This works fine when
HasDomAttrs#dom_data returns a fresh mutable hash, but breaks when the
upstream base becomes a frozen shared constant (see tomasc/has_dom_attrs#2,
where EMPTY_HASH is returned to eliminate per-call allocations for
components that don't override).
Switching to `current.merge(k => v)` preserves behavior and works against
both the old mutable base and the new frozen base. No extra allocation in
the common case because the previous pattern also allocated a hash at the
bottom of the super chain.
All 71 existing assertions pass (1 pre-existing skip).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
* Add CHANGELOG entry for non-mutating prepend pattern
* Update has_stimulus_attrs.gemspec
---------
Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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Summary
Cuts ~1.5–2 MB of allocations per heavy page render (measured on rijksakademie.nl via MemoryProfiler) by:
dom_classes,dom_aria,dom_data,dom_stylereturn shared frozen constants instead of fresh empty collections per call.super().tap { mutate }to non-mutatingsuper() + [v]/super().merge(name => v)so the frozen bases are safe.dom_attrsto avoid the 4-allocation.reject.deep_stringify_keys.deep_transform_keyschain — now oneresult = {}with conditional per-slot assignments.DomStyle#mergeadded so thathas_dom_stylechained prepends still returnDomStyle(not a plainHash).Behavioral parity
dom_attrsis functionally identical: top-level keys as strings ("aria"/"class"/"data"/"style"), nested keys dasherized, empty slots omitted.has_dom_classstill resolves Proc/Symbol/literal values and appends to the class list.if:/unless:short-circuiting preserved.Why
On a 400-component page the old base allocated ~1600 empty collections no one ever used (half the components never set
dom_aria/dom_data/etc.). Line 118 (DomStyle.new({})) alone showed up at 404 kB in the allocation profile; the gem as a whole at 2.36 MB.Post-change, components that don't opt in pay zero; components that do pay the same as before.
Test plan
MemoryProfiler.reporton rijksakademie.nl after bump — expect gem allocation drop of ~1.5–2 MB🤖 Generated with Claude Code