03-structs

Example 03: Struct-Based Configuration

Using Go structs to define and load configuration.

What This Shows

• Defining configuration as nested structs
• Using mapstructure tags for field mapping
• Loading from nested maps with FromMap
• Unmarshaling to structs with type conversion
• Automatic handling of durations and other types

Running

go run main.go

Key Points

1. Struct Definition - Configuration schema defined as Go structs
2. Mapstructure Tags - Control how fields map to configuration keys
3. FromMap - Convert nested maps to flat key-value pairs
4. Type Safety - Automatic conversion to correct Go types
5. Nested Structures - Support for complex configuration hierarchies

Type Conversions

The library automatically handles common conversions:

• String "true"/"false" → bool
• String numbers → int, float64
• Duration strings → time.Duration (e.g., "30s", "5m")
• String values → appropriate types based on struct fields

Configuration Keys

The struct fields map to flat keys:

• Config.App.Name → app.name
• Config.Server.Port → server.port
• Config.Database.MaxConns → database.max_conns

Output Example

=== Loaded Configuration ===
App:
  Name: MyApplication
  Version: 1.0.0
  Debug: true

Server:
  Host: 0.0.0.0
  Port: 9000
  Read Timeout: 30s
  Write Timeout: 30s

Database:
  Host: db.example.com
  Port: 5432
  Database: myapp
  User: appuser
  Max Connections: 50