Ad hoc type design

[bvssvni]

Dyon supports types that are ad-hoc, or partially defined. An ad-hoc type can have any name not used by other Dyon types. It is common to use CamelCase.

An ad-hoc type has an optional inner type where you put more details about the type. When not specified, this is set to {}. For example Person and Person {} is the same type.

An ad-hoc type is not declared, but written directly in the function declaration.

Example:

fn new_person(name: str) -> Person {
    return { name: name }
}

The inner type goes with the ad-hoc type and vice versa. An error is shown if you try to use a different ad-hoc type or a different inner type where an ad-hoc type is expected.

Addition and multiplication

Two ad-hoc types can be added if the inner type allows addition.

Dyon complains if you try to add an ad-hoc type with an inner type.

For example:

// Convert number to `km`
fn km(v: f64) -> km f64 { return v }

km(3) + km(4) // OK
km(3) + 4 // ERROR

Before #638, multiplication is not allowed, because this often changes physical units.

After #638, multiplication is allowed, because one can override the multiplication operator to deal with physical units.