Primitives and literals

Integer and float types

There is no int, no long, no byte. The size is part of the name.

f16 is the IEEE half-precision float (2 bytes), primarily a storage type for ML and graphics data. It converts to and from the wider floats with as (hardware fpext / fptrunc), and exposes a bit-preserving reinterpret to and from its raw u16:

let h: f16 = 1.5f32 as f16;          // fptrunc
let x: f32 = h as f32;               // fpext

let h2: f16 = f16::from_bits(0x3C00 as u16);   // IEEE half 1.0
let raw: u16 = h2.to_bits();

Arithmetic on f16 works, but the idiomatic hot-path pattern is to convert to f32, compute, then convert back.

Other primitives

• bool: true / false. It cannot be produced by an integer cast.
• (): the unit type, the implicit return of a function with no arrow.
• str: a string view (pointer plus length), borrowed. A built-in type.
• *T: a raw pointer. Operations require unsafe.
• fn(...) -> R: a function pointer.

The owned, growable string is not a primitive: it is Text, a plain standard-library type (stdlib/text). The compiler knows it only through a single lang-item, so even the string lives in a package. A file that names an owned string, or uses interpolation, imports it:

import "stdlib/text" as text;

let mut s: text::Text = text::from_str("hello");
s.push_str(", world");

.to_string() and string interpolation produce a Text and work without the import (the value is just un-nameable until you import the type). A single-file program that only needs borrowed views uses str.

Literals

let a: i32 = 42;
let b: u64 = 42u64;            // typed literal
let c: f64 = 3.14;
let d: bool = true;
let e: str = "hello";
let f: i32 = 0x1F;             // hex
let g: i32 = 0b1010;           // binary
let h: i32 = 1_000_000;        // underscore separators

A """...""" literal is a multi-line string, taken verbatim: no indentation stripping and no escape processing, so the bytes between the triple quotes are exactly the value.

let shader: str = """
#version 450
layout(location = 0) in vec3 pos;
void main() { gl_Position = vec4(pos, 1.0); }
""";

Character literals: 'a' is a u8 byte literal, a shorter way to write 97u8. The backslash escapes '\n', '\t', '\r', '\\', '\'', '\"', '\0', and the hex form '\xFF' all work. A multi-byte UTF-8 codepoint such as 'á' is rejected at parse time, since the type is u8, not a full Unicode codepoint. For UTF-8 use a str.