Guides generic vs trait object decisions in Rust. Use when choosing between static and dynamic dispatch, designing traits, handling E0277/E0038, or deciding between enum and dyn Trait.
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Layer 1: Language Mechanics
Do we need compile-time or runtime polymorphism?
Before choosing between generics and trait objects:
Before adding trait bounds:
What abstraction is needed?
When is type known?
What's the trade-off priority?
// Static dispatch — type known at compile time
fn process(x: impl Display) { } // argument position
fn process<T: Display>(x: T) { } // explicit generic
fn get() -> impl Display { } // return position
// Dynamic dispatch — type determined at runtime
fn process(x: &dyn Display) { } // reference
fn process(x: Box<dyn Display>) { } // owned
| Scenario | Choose | Why |
|---|---|---|
| Performance critical | Generics | Zero runtime cost |
| Heterogeneous collection | dyn Trait | Different types at runtime |
| Plugin architecture | dyn Trait | Unknown types at compile time |
| Reduce compile time | dyn Trait | Less monomorphization |
| Small, known type set | enum | No indirection |
| Pattern | Dispatch | Code Size | Runtime Cost |
|---|---|---|---|
fn foo<T: Trait>() | Static | +bloat | Zero |
fn foo(x: &dyn Trait) | Dynamic | Minimal | vtable lookup |
impl Trait return | Static | +bloat | Zero |
Box<dyn Trait> | Dynamic | Minimal | Allocation + vtable |
A trait is object-safe if it:
Self: Sized boundSelfwhere Self: Sized for non-object-safe methods| Error | Cause | Fix |
|---|---|---|
| E0277 | Type doesn't impl trait | Add impl or change bound |
| E0308 | Type mismatch | Check generic params |
| E0599 | No method found | Import trait with use |
| E0038 | Trait not object-safe | Use generics or redesign |
| Anti-Pattern | Why Bad | Better |
|---|---|---|
| Over-generic everything | Compile time, complexity | Concrete types when possible |
dyn for known types | Unnecessary indirection | Generics |
| Complex trait hierarchies | Hard to understand | Simpler design |
| Ignore object safety | Limits flexibility | Plan for dyn if needed |
type-driven-design — newtypes and type stateperformance — when dispatch cost mattersconcurrency — Send/Sync bounds on generics还没有评价。欢迎分享你的使用感受。
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Add an iOS App Clip target to an Expo app. Use when the user mentions App Clip, AASA, apple-app-site-association, appclips, smart app banner, or wants to ship a lightweight iOS Clip invoked from a URL alongside their parent app.
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Automates browser interactions for web testing, form filling, screenshots, and data extraction. Use when the user needs to navigate websites, interact with web pages, fill forms, take screenshots, test web applications, or extract information from web pages.
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Add Agentation visual feedback toolbar to a Next.js project
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Apple's approach to interface design and fluid, physical motion, translated for the web. Use when building or reviewing gesture-driven UI, spring animations, drag/swipe/sheet interactions, momentum and interruptible transitions, translucent materials and depth, typography (optical sizing, tracking, leading), reduced-motion, or the design foundations (feedback, spatial consistency, restraint) behind Apple-style interfaces.
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Derive and implement first-principles audio-coupled haptic and kinetic UI feedback. Use when designing, reviewing, or coding haptics/audio for mobile apps, native iOS/Android, React Native/Expo, SwiftUI, games, detent pickers, toggles, sliders, page curls, scroll gestures, wallet/signature flows, Solana transactions, backend/realtime state changes, confirmations, settlements, and semantic UI events where feedback should follow signal math instead of ad hoc vibration calls.
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Babysit a GitHub pull request during a user-approved monitoring window by polling review comments, CI checks/workflow runs, and mergeability state. Diagnose failures, retry likely flaky failures up to 3 times, auto-fix/push branch-related issues when appropriate, and report fresh review feedback. Use when the user asks Codex to monitor a PR, watch CI, handle review comments, or keep an eye on failures and feedback on an open PR.
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