ffi-designer
Skill17 starsChanged 9 months agoApache-2.0View on GitHub
Design and implement Foreign Function Interfaces for calling code in other languages.
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The file
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2 rules. About 0 are common, 2 are distinctive, and 0 are very specific to this project.
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- Common
- Distinctive
- Very specific
- Distinctive: line 43
Use binding generators for large libraries
- Distinctive: line 84
When performance isn't critical
≈ “Common” is an estimate: at least 1 in 5 of the 350,495 skill files we read have a rule of the same kind, not the same words. “Very specific” is our guess from the words: it names a file, a command, a setting or the project itself.
Files
FFI Designer
Foreign Function Interfaces (FFI) enable programs to call code written in other languages. They bridge language runtimes and enable reuse of existing libraries.
When to Use This Skill
- Calling C libraries from high-level languages
- Interoperability between language runtimes
- Binding generation
- Performance-critical interop
- Embedding interpreters
What This Skill Does
- Type Mapping: Convert types between languages
- Calling Convention: Handle ABI differences
- Memory Management: Manage memory across boundaries
- Callback Support: Allow foreign code to call back
- Error Handling: Propagate exceptions across FFI
Key Concepts
| Concept | Description |
| ABI | Application Binary Interface |
| Calling Convention | How parameters are passed |
| Type Marshalling | Convert types across boundaries |
| Callback | Function pointer passed to foreign code |
| Binding | Glue code for FFI |
Tips
- Use binding generators for large libraries
- Handle memory ownership carefully
- Document ownership semantics
- Test with sanitizers
- Consider thread safety
Common Use Cases
- Calling C libraries
- System programming
- Performance-critical code
- Native GUI bindings
- Game engine integration
Related Skills
llvm-backend-generator- Generate FFI codetype-checker-generator- Type-safe FFImemory-allocator- Memory management
Canonical References
| Reference | Why It Matters |
| ctypes documentation | Python FFI |
| JNI specification | Java Native Interface |
| "FFI and PL design" papers | Design principles |
Tradeoffs and Limitations
Approach Tradeoffs
| Approach | Pros | Cons |
| ctypes | Simple, Python | Slow |
| cffi | Fast | More complex |
| Native bindings | Fastest | Language-specific |
When NOT to Use This Skill
- Pure language code
- When performance isn't critical
- Cross-platform portability required
Limitations
- ABI compatibility issues
- Platform-specific behavior
- Complex type mappings
Assessment Criteria
A high-quality implementation should have:
| Criterion | What to Look For |
| Type Safety | Correct type mappings |
| Memory Safety | Proper ownership |
| Performance | Minimal overhead |
| Usability | Easy to use |
Quality Indicators
✅ Good: Type-safe, handles memory correctly, clean API ⚠️ Warning: Some manual memory management needed ❌ Bad: Type-unsafe, memory leaks, crashes
Research Tools & Artifacts
Real-world FFI systems:
| Tool | Why It Matters |
| cffi (Python) | C FFI for Python |
| JNI | Java Native Interface |
| SWIG | Simplified wrapper generator |
| clang bindings | LLVM-based FFI |
Key Systems
- GHC Haskell FFI: Type-safe FFI
- Rust FFI: Safe FFI with ownership
Research Frontiers
Current FFI research:
| Direction | Key Papers | Challenge |
| Safe FFI | "Safe FFI" (2018) | Memory safety |
| Zero-cost | "Zero-cost FFI" | Performance |
| Bidirectional | "Foreign函" | Two-way interop |
Hot Topics
- WebAssembly FFI: Wasm FFI design
- Multi-language runtimes: GraalVM polyglot
Implementation Pitfalls
Common FFI bugs:
| Pitfall | Real Example | Prevention |
| Memory leaks | Not freeing native memory | Ownership rules |
| Type mismatches | Wrong ABI | Use bindings |
| GC issues | GC collected native pointer | Keep reference |
| Encoding | String encoding issues | Use proper encoding |
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