Default Values

The syntax schema Name { field: Type = default } associates a default value with each field. Calling Name.default() returns an instance with all fields filled in — no arguments, no map, no validation. It is the right choice for configurations and request objects where "the initial state is already meaningful".

Config.default() fills in port, host, and debug mode without any arguments.

01-defaults.zolo

Playground

// Feature: schema with default values — `Schema.default()` builds an instance
// Syntax: `schema Name { field: type = default, ... }`. Calling
// `Name.default()` returns an instance with every field set.
// When to use: configs, settings, request bodies — when "the default
// shape is meaningful and you want zero-arg construction".

schema Config {
  port: int = 8080,
  host: str = "localhost",
  debug: bool = false,
}

let cfg = Config.default()
print(cfg.port)

// expected: 8080
print(cfg.host)

// expected: localhost
print(cfg.debug)

// expected: false

// Fields are accessed like struct fields.
print("listening on {cfg.host}:{cfg.port}")
// expected: listening on localhost:8080

Challenge

Add a field timeout: int = 30 to the Config schema and print cfg.timeout. What happens if you remove the default value and call Config.default() again?