df_03_defaults

configuration defaults with merge

this example demonstrates how to build robust configuration systems using df.Merge(). unlike df.Bind() which overwrites the entire struct, Merge() intelligently overlays external data onto pre-initialized structs with sensible defaults.

key concepts demonstrated

defaults systems

• pre-initialized structs: start with sensible default values
• selective overrides: external config only specifies what should change
• preserved defaults: unspecified fields keep their original values
• layered configuration: multiple sources can be merged progressively

configuration hierarchies

• layer 1: application defaults (compiled into code)
• layer 2: environment-specific config (dev/staging/prod)
• layer 3: user overrides (CLI flags, user preferences)
• final result: intelligent merge of all layers

real-world patterns

• 12-factor app compliance: environment-based configuration
• backward compatibility: new fields with defaults don't break existing configs
• progressive enhancement: users can adopt new features gradually
• ops-friendly: minimal config files, maximum flexibility

workflow demonstrated

1. initialize with defaults: create structs with sensible default values
2. apply partial config: use df.Merge() to overlay external configuration
3. verify preservation: show which values were overridden vs preserved
4. configuration layering: demonstrate multiple merge operations

example structure

// Application defaults (compiled-in)
config := &AppConfig{
    Server: ServerConfig{
        Host:    "localhost",
        Port:    8080,
        Timeout: 30,
        Debug:   false,
    },
    Database: DatabaseConfig{
        Host:     "localhost", 
        Port:     5432,
        Database: "myapp",
        SSL:      true,
    },
}

// Partial override (from config file/env/CLI)
partialData := map[string]any{
    "server": map[string]any{
        "host":  "api.example.com",
        "debug": true,
        // port and timeout not specified - will be preserved
    },
}

// intelligent merge
df.Merge(config, partialData)

running

go run main.go

the output clearly shows which values were updated from external config and which defaults were preserved, demonstrating the power of selective configuration merging.