Defaults

Use the default tag to make a field usable when no higher-priority source supplied it.

type Config struct {
    Host    string `default:"localhost"`
    Port    int    `default:"8080"`
    Enabled bool   `default:"true"`
}

Fuda converts the tag value to the field's Go type. For example, default:"8080" becomes an int for Port.

Defaults fill missing values

This YAML file leaves port out:

host: 0.0.0.0

The resulting configuration has Host set to 0.0.0.0 and Port set to 8080.

Fuda does not replace a value that the file supplied. These values stay exactly as written:

port: 0
enabled: false
host: ""

Use null when you want a YAML key to behave as missing:

port: null

Fuda then applies the default value for Port.

When to use a default

Choose defaults that make local development straightforward. Require an environment variable or validation rule for values that production must provide.

Next step

Override configuration with environment variables.