LazyGophers Utils
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      • defaults - Default Values

      Overview

      The defaults module provides default value setting for Go structs with support for various data types and custom default functions.

      Functions

      SetDefaults()

      Set default values for a struct.

      func SetDefaults(value interface{}, opts ...Options) error

      Parameters:

      • value - Struct pointer to set defaults for
      • opts - Options for default behavior

      Options:

      • ErrorMode - Error handling mode (Panic, Ignore, Return)
      • ValidateDefaults - Whether to validate default values
      • AllowOverwrite - Whether to allow overwriting non-zero values

      Example:

      type Config struct {
    Host     string `default:"localhost"`
    Port     int    `default:"8080"`
    Debug    bool   `default:"false"`
    Timeout  int    `default:"30"`
}

var cfg Config
defaults.SetDefaults(&cfg)
// cfg.Host == "localhost"
// cfg.Port == 8080
// cfg.Debug == false
// cfg.Timeout == 30

      RegisterCustomDefault()

      Register custom default function for a type.

      func RegisterCustomDefault(typeName string, fn DefaultFunc)

      Parameters:

      • typeName - Type name for registration
      • fn - Default function

      Example:

      defaults.RegisterCustomDefault("time.Time", func() interface{} {
    return time.Now()
})

      Usage Patterns

      Struct Initialization

      type User struct {
    Name     string `default:"Anonymous"`
    Email     string `default:""`
    Age       int    `default:"0"`
    Active    bool   `default:"true"`
    CreatedAt time.Time `default:"now"`
}

var user User
defaults.SetDefaults(&user)
// user.Name == "Anonymous"
// user.Email == ""
// user.Age == 0
// user.Active == true
// user.CreatedAt == time.Now()

      Custom Defaults

      type Product struct {
    Name     string
    Price     float64
    Stock     int
    Category  string
}

defaults.RegisterCustomDefault("Product.Price", func() interface{} {
    return 0.0
})

defaults.RegisterCustomDefault("Product.Stock", func() interface{} {
    return 100
})

var product Product
defaults.SetDefaults(&product)
// product.Price == 0.0
// product.Stock == 100

      Error Handling

      // Good: Panic on error
defaults.SetDefaults(&cfg, defaults.Options{
    ErrorMode: defaults.ErrorModePanic,
})

// Good: Ignore errors
defaults.SetDefaults(&cfg, defaults.Options{
    ErrorMode: defaults.ErrorModeIgnore,
})

// Good: Return errors
defaults.SetDefaults(&cfg, defaults.Options{
    ErrorMode: defaults.ErrorModeReturn,
})

      Best Practices

      Default Tags

      // Good: Use appropriate default values
type Config struct {
    Host     string `default:"localhost"`  // Good default
    Port     int    `default:"8080"`   // Good default
    Debug    bool   `default:"false"`   // Good default
    Timeout  int    `default:"30"`     // Good default
}

// Avoid: Unnecessary defaults
type Config struct {
    Host     string `default:""`         // Bad default
    Port     int    `default:"0"`         // Bad default
    Debug    bool   `default:"false"`   // Good default
}