[makspll]

ui.each(items, function(item) .. end): a region with one child per item of the list held by a signal. Children are kept by item (the item is the key, as key is for ui.el), so the function only runs for items which were not in the list before. A ui.dynamic list re-runs the whole loop on every change: one ui.el call and props conversion per row, kept or not.

ui.each(visible, function(name)
    return ui.el(Slot, { name = name, entity = entities[name], selected = is_selected, on_select = select })
end)

• What the function reads is not tracked: it builds a child once. When the parent renders again (i.e. a reload) the kept children are built again and patched, as ui.dynamic does.
• The inventory test and benches use it for their list, ui.dynamic stays covered by the other regions.
• New bench scenario inventory add or remove one.

Stacked on #719.

Measured on a local merge with #720 and #721, prebuilt binaries, 3 alternating rounds (Closures):

bench	ui.dynamic	ui.each
one row removed or added, of 200	686 µs	109 µs (−84%)
inventory search (162 of 200 rows change)	1.78 ms	1.72 ms
inventory mount or unmount 200	2.02 ms	2.05 ms

It only helps when most rows stay. What is left of the one row case is the list of 200 names itself: it crosses to Rust when computed, back to Lua for the title, and is keyed in Rust.

[semanticdiff-com]

Review changes with  

Changed Files

File	Status
assets/tests/reactive_ui/inventory/inventory.lua	45% smaller
crates/bevy_mod_scripting_reactive_ui/src/element.rs	39% smaller
assets/macro_benchmarks/reactive_ui/closures.lua	37% smaller
assets/macro_benchmarks/reactive_ui/paths.lua	37% smaller
crates/bevy_mod_scripting_reactive_ui/src/runtime.rs	5% smaller
benches/benchmarks.rs	0% smaller
crates/bevy_mod_scripting_reactive_ui/src/lib.rs	0% smaller

[github-actions]

Bencher Report

Project	Bevy Scripting
Branch	agent/reactive-ui-each
Testbed	linux-gha

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