IDL / Schema

The Interface Description Language (IDL, also called the schema) is what you write by hand. A schema file has the extension .ids and lives under a project's src/ directory. It defines the data shapes and the protocols that carry them, independent of any language.

greeting.ids

const GREETING_MAX: u16 = 280

enum Language {
    English
    Spanish
    Japanese
}

/// A greeting in a given language.
struct Greeting {
    message: char[max GREETING_MAX]
    language: Language
    optional sender: char[max 64]
}

protocol Greeter {
    function greet(greeting: Greeting) -> bool;
}

Declarations

A schema is a flat list of declarations, in any order:

Keyword	Purpose
`struct`	a data shape — named, typed fields
`enum`	a closed set of named variants
`protocol`	a set of callable `function`s
`error`	a named failure with an interpolated `message` and fields, raised by functions with `!`
`const`	a compile-time constant: `const NAME: type = value`
`type`	a second name for a type: `type UserId = u64`
`settings`	package/schema-wide authoring policy (`key = value`) — enforced at build time
`validator`	a named, parameterised check on a field's value, run by generated code
`use`	pull declarations in from another schema or package

Annotations

A line @key = value above a declaration, field or function configures it: @validators, @framing, @deprecated and others. See Annotations.

Comments and docs

// is a comment. /// lines are docstrings and attach to the next declaration. //! lines at the top of a file are its module docs.

Imports

imports.ids

use std::http::Request
use mypackage::{User, Post}
use external::uuid::Uuid as UUID
use parent::common::*

self::, parent:: and package:: prefixes resolve relative to the current schema. See Imports.