1# Demystify SwiftUI Performance (WWDC23) (Summary)
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3Context: WWDC23 session on building a mental model for SwiftUI performance and triaging hangs/hitches.
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5## Performance loop
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7- Measure -> Identify -> Optimize -> Re-measure.
8- Focus on concrete symptoms (slow navigation, broken animations, spinning cursor).
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10## Dependencies and updates
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12- Views form a dependency graph; dynamic properties are a frequent source of updates.
13- Use `Self._printChanges()` in debug only to inspect extra dependencies.
14- Eliminate unnecessary dependencies by extracting views or narrowing state.
15- Consider `@Observable` for more granular property tracking.
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17## Common causes of slow updates
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19- Expensive view bodies (string interpolation, filtering, formatting).
20- Dynamic property instantiation and state initialization in `body`.
21- Slow identity resolution in lists/tables.
22- Hidden work: bundle lookups, heap allocations, repeated string construction.
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24## Avoid slow initialization in view bodies
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26- Don’t create heavy models synchronously in view bodies.
27- Use `.task` to fetch async data and keep `init` lightweight.
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29## Lists and tables identity rules
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31- Stable identity is critical for performance and animation.
32- Ensure a constant number of views per element in `ForEach`.
33- Avoid inline filtering in `ForEach`; pre-filter and cache collections.
34- Avoid `AnyView` in list rows; it hides identity and increases cost.
35- Flatten nested `ForEach` when possible to reduce overhead.
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37## Table specifics
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39- `TableRow` resolves to a single row; row count must be constant.
40- Prefer the streamlined `Table` initializer to enforce constant rows.
41- Use explicit IDs for back deployment when needed.
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43## Debugging aids
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45- Use Instruments for hangs and hitches.
46- Use `_printChanges` to validate dependency assumptions during debug.
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