Type Enums ​

Type enums give you sum type functionality. Sum types are actually treated as any, but they are safer. Just like an any type, its default value is always nil and nil must be checked. Only data compatible with the types set are allowed to be retained, other data types are not accepted. It is strict about type safety, even implicit casting is not accepted, type must be explicitly compatible.

Declaring a type-enum is easy. Declare it just like an enum. Just say the enum field type is type.

For example:

enum Signed: type {
    I8: i8,
    I16: i16,
    I32: i32,
    I64: i64,
}

You can also write only the types you want for the sum type without using a named field.

For example:

enum Signed: type {
    i8,
    i16,
    i32,
    i64,
}

There must always be at least one field. Other fields can point to the enum itself (which is bad practice but allowed) but there is one exception; If there is only one field and it points to its own type-enum declaration, this will lead to a pointless loop, so your compiler won't allow it.

Each field must have an explicit type declaration. For type safety, any of the fields are not allowed to point to type any.

They can be used in match-type expressions. But they can only map to the types they support. Likewise, cast expressions can only be cast with the types they support.

In binary expressions, only compatible types can be used. And the only supported operators are == and != operators.

With the advantage of being an enum, you can also use it for side purposes such as grouping types. When you use the type itself, you get a sum type that fits all of them collectively. However, when you treat it as a field, you get the type that that field points to.

For example:

enum Types: type {
    Bool: bool,
    String: str,
}

fn main() {
    let x: Types = "hello world"
    println(x)
    let y: Types.String = "hello world"
    println(y)
}

At example above, the variable x is Types, so it's type is Types.Bool or Types.String and handled as any at runtime. But the variable y is actual str type and handled as str at compile-time and runtime.

Type Inheritance ​

Type enums can inherit each other. To do this, give a type enum a different type enum as a field. From this point on, the other type enum will be supported directly and all fields of the other type enum will also be supported by inheriting.

For example:

enum Signed: type {
    int,
}

enum Unsigned: type {
    uint,
}

enum Int: type {
    Signed,
    Unsigned,
}

fn main() {
    let a: Int = 20
    println(a)
}

In the example above, Int does not directly support the int type. However, the Signed enum it supports includes support for int. So Int supports the int type which it inherits from.