Golang Patterns

# Go Patterns

> This skill provides comprehensive Go patterns extending common design principles with Go-specific idioms.

## Functional Options

Use the functional options pattern for flexible constructor configuration:

```go
type Option func(*Server)

func WithPort(port int) Option {
    return func(s *Server) { s.port = port }
}

func NewServer(opts ...Option) *Server {
    s := &Server{port: 8080}
    for _, opt := range opts {
        opt(s)
    }
    return s
}
```

**Benefits:**
- Backward compatible API evolution
- Optional parameters with defaults
- Self-documenting configuration

## Small Interfaces

Define interfaces where they are used, not where they are implemented.

**Principle:** Accept interfaces, return structs

```go
// Good: Small, focused interface defined at point of use
type UserStore interface {
    GetUser(id string) (*User, error)
}

func ProcessUser(store UserStore, id string) error {
    user, err := store.GetUser(id)
    // ...
}
```

**Benefits:**
- Easier testing and mocking
- Loose coupling
- Clear dependencies

## Dependency Injection

Use constructor functions to inject dependencies:

```go
func NewUserService(repo UserRepository, logger Logger) *UserService {
    return &UserService{
        repo:   repo,
        logger: logger,
    }
}
```

**Pattern:**
- Constructor functions (New* prefix)
- Explicit dependencies as parameters
- Return concrete types
- Validate dependencies in constructor

## Concurrency Patterns

### Worker Pool