r3bl-open-core: Skill for Claude Code

Fast String Allocations & Zero-Overhead Formatting

When writing code that involves string building, formatting, or rendering (especially in the TUI engine, logging, or event loops), you MUST adhere to the codebase's strict zero-allocation architecture.

When to Use

• When building ANSI escape sequences
• When building strings in a 60 FPS event loop or render cycle
• When using tracing::*! macros
• Whenever you are tempted to use format! or write! on a Formatter

Core Strategy

Read the full Source of Truth at mod@crate::core::common::fast_strings#string-allocation-performance-strategy for detailed architectural constraints.

Performance Hierarchy (Fastest to Slowest)

1. Direct push_str() - Zero overhead, direct memory copy.
2. crate::format_no_alloc! - Zero heap allocations, reuses existing heap.
3. FastStringify - Temporary heap allocation, completely bypasses Formatter state machine.
4. inline_string! - Stack allocated (16 bytes), but dynamically spills to the heap if exceeded.
5. format! / write! - Always heap allocates (format!) OR uses heavy formatter overhead (write!). Avoid in hot paths.

Implementation Guidelines

1. The FastStringify Trait

Use for custom types (like ANSI codes) that are serialized millions of times.

• Bypasses the expensive Formatter state machine by pushing everything into a temporary heap String and making ONE f.write_str() call.
• Use generate_impl_display_for_fast_stringify! to auto-generate the Display block.

2. The inline_string! Macro

Use for stack-allocated strings (16 bytes).

• Drop-in replacement for format!.
• The primary use case is the core Editor Component and tracing::*! macros.
• Warning: If text exceeds 16 bytes, it spills to the heap and incurs the cost of format!.

3. The format_no_alloc! Macro

Use for hot loops where the string is guaranteed to exceed 16 bytes (meaning inline_string! would spill).

• Hoist a String::with_capacity(N) outside the loop.
• Pass the hoisted string into the macro inside the loop to clear and write into the existing capacity.
• Zero allocations per tick.