Type¶

A type is a description of a set of values and a set of operations on those values.

A value is an instance of a specified type; for example 42 is an instance of type i32.

User-defined types¶

You can define your own types using the type declaration syntax.

type Book {
    page_count: u32;
}

type Magazine {
    page_count: u32;
}

Predefined types¶

Some types are not a set of values of other types, but values in themselves.

Most of the predefined types are:

1. Contain a number — this number describes how many bits the type value takes in memory.
2. Lowercase — they are all keywords, and just a shortcut to their full name.

You probably thought that user-defined and predefined are very separate categories of types. This is not the case. In reality predefined type i32 corresponds to user-defined type SInteger32 in the standard library. The key difference is that predefined types are more controlled by the compiler than by the user.