Supertypes, Subtypes, & Type Coercion

Types are able to automatically be coerced into their supertypes.

main {
    let bar: uint = 10;
    let foo: int = bar; // `uint` is a subtype of `int`, so it can be coerced to type `int`
}

Array Types

An array type A is a subtype of another array type B if:

1. The element type of A is a subtype of the element type of B
2. The two array types are the same length

main {
    let ints: [int; 5] = [1, 2, 3, 4, 5];
    let nums: [num; 5] = ints;
}

Struct Types

A struct type A is a subtype of another struct type B if:

1. A & B share the same number of fields, with the same names, in the same order
2. The type of a given field in A is a subtype of that same field's type in B

main {
    let coords: { x: num, y: num } = { x: 1.1, y: -2 };
    let vals: { x: val, y: val } = coords;
}

Reference Types

A reference type &A is a subtype of another reference type &B only if A & B are isomorphic, meaning A is a subtype of B and B is a subtype of A.