Introduction
Go is known for simplicity, but sometimes you need more flexibility. Reflection lets you inspect types and values at runtime, while code generation creates Go code automatically. Both techniques help eliminate repetitive code and build more flexible systems.
When You Need These Techniques
Most Go code doesn’t need reflection or code generation. But they’re valuable when:
- Building frameworks: ORMs, web frameworks, and serialization libraries
- Eliminating boilerplate: Generating repetitive struct methods
- Dynamic behavior: Handling unknown types at runtime
- API tooling: Generating client libraries from definitions
- Testing utilities: Creating mocks and test helpers
Reflection vs Code Generation
Reflection happens at runtime:
- Inspect types and values dynamically
- Call methods by name
- Access struct fields programmatically
- Slower performance, less type safety
Code Generation happens at build time:
- Generate Go source code automatically
- Full type safety and performance
- Requires build-time tooling
- More complex setup
Common Use Cases
Reflection Examples:
- JSON marshaling/unmarshaling
- Struct validation
- Dependency injection
- Generic algorithms (before Go 1.18)
Code Generation Examples:
- Protocol buffer compilers
- Mock generators
- Enum string methods
- Database query builders
Trade-offs to Consider
Both techniques have costs:
- Complexity: Harder to understand and debug
- Performance: Reflection is slower than direct code
- Type Safety: Reflection can panic at runtime
- Tooling: Code generation requires build integration
This guide covers when and how to use these powerful techniques effectively.