Each named type application must supply exactly the declared number of type arguments. This applies to opaque types, built-in types, parameters, and nested applications; a type parameter takes zero arguments.

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A struct or enum can carry triple-quoted prose immediately inside its opening brace. The parsed declaration retains that text; omitting it is permitted.

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An enum contains named variants in source order. A variant can have no payload, an ordered tuple payload, or named, typed fields. These three shapes remain distinct, including when a tuple or named payload is empty.

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A named field can carry triple-quoted prose immediately before its name. The parsed field retains that text independently of the containing declaration or variant’s prose. At the start of a body, the first prose string describes the container; a description for its first field follows as a second string.

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Structs, enums, and opaque types can declare a nonempty comma-separated list of type parameters in angle brackets. Parameters are available throughout their own declaration and do not become names in other declarations.

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Adjacent named fields, enum variants, and tuple payload elements require a comma separator. A trailing comma before the closing delimiter is optional.

For example:

type Binder<T> {
    """A value under the generic parameters binding its references."""
}

struct Items {
    items: Vec<crate::symbols::Symbol>,
}

enum MethodReceiver {
    Value { mutable_binding: bool },
    Ref {
        """A borrowed receiver with the declared mutability."""
        mutability: Mutability,
    },
}

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An unqualified type name resolves first to a parameter of its declaration, then to a type, class, or context in the same module, then to the built-in prelude. An earlier match shadows a later one.

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An opaque type declares a name and any type parameters without fields or variants. It requires triple-quoted descriptive prose, either inside braces or before a terminating semicolon. A payload inside its body is an error.

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The built-in prelude contains Vec<T>, Option<T>, bool, u32, u64, and String. These names are available without declaring them in the model.

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A type outside the current module requires a crate:: or $cratename:: qualified path. Cross-crate type references require a declared dependency; unqualified lookup does not search other modules or the crate root.

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Semantic value types can refer directly to themselves or to each other, without Box or another storage indirection. Such recursion is not a validation error.

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A struct contains named, typed fields. The parsed declaration retains their names, types, and source order; an empty struct is permitted.

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Parentheses always denote a tuple, including () and a single element with or without a trailing comma. (T) is distinct from T when result types are compared for an override.

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Type expressions are named types with optional generic arguments, or tuples. Generic arguments and tuple elements are themselves type expressions, allowing arbitrary nesting. The parsed expression retains that nesting.

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Named fields have distinct names within a struct or a single enum variant. Different declarations and different variants may reuse field names.

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A value declaration cannot repeat a type parameter’s name.

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Variants have distinct names within an enum. Different enums may reuse a variant name.

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Every type name in a value field, variant payload, class or context field, or method result must resolve. An unknown name is an error even when nested in generic arguments or tuples.

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A variant can carry triple-quoted prose immediately inside its payload’s opening delimiter, or immediately after a unit variant’s name. The parsed variant retains that text independently of other variants.

Read in specification context