Structure

A structure (struct, also called a message) is a named data shape. It carries typed fields.

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struct Message {
    sender: string
    recipient: string
    body: string
    priority: u8
}

Fields

A field is name: Type, one per line, in declaration order. A field may be marked optional and may carry a default.

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struct Message {
    body: string
    optional subject: string
    priority: u8 = 1
    language: Language = default
}

• optional — the field may be absent. Without it, the field is required.
• = <value> — a default. Any value form a constant accepts — a literal, another constant by name, a ::-path, or an f-string — plus the bare word default (the type's own default, e.g. an enum's first variant). Non-literals are recorded but not resolved yet.

Field types

Use string for text; str and String are not Comline types — see Text.

Docstrings

A docstring (/// lines) and @key=value annotations attach to a struct or an individual field.

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/// A message routed through the mail protocol.
struct Message {
    body: string

    /// Shown in the client's list view.
    optional subject: string
}

Annotations

An annotation's value is one of three forms:

• A single value: an integer, a string, true/false or a name (@timeout_ms = 1000).
• A list of calls, for @validators (@validators = [StringBounds(min_chars = 3)]).
• A dictionary of key = value entries, for an annotation with several settings, such as @framing (@framing = { name = "jsonrpc", method_names = qualified }).

struct Message {
    @optional // <- This is an annotation
    body: string
}

TODO: annotations might not apply to structures, only fields