Crate four_cc

Newtype wrapper providing a convenient representation of four-character-code values.

Using this type in a public APIs as an alternative to simply passing the equivalent u32 makes the value’s expected use explicit.

Creating a FourCC value

use four_cc::FourCC;

let uuid = FourCC(*b"uuid");

From a slice

let data = b"moofftyp";
let code = FourCC::from(&data[0..4]);  // would panic if fewer than 4 bytes
assert_eq!(FourCC(*b"moof"), code);

Constants

FourCC values can be used in const expressions

const UUID: FourCC = FourCC(*b"uuid");

Matching

You can use FourCC values in match patterns as long as you define constants to match against,

const UUID: FourCC = FourCC(*b"uuid");
const MOOV: FourCC = FourCC(*b"moov");
match other_value {
    MOOV => println!("movie"),
    UUID => println!("unique identifier"),
    // compiler will not accept: FourCC(*b"trun") => println!("track fragment run"),
    _ => println!("Other value; scary stuff")
}

Invalid literal values

If the literal has other than four bytes, compilation will fail

let bad_fourcc = FourCC(*b"uuid123");
// -> expected an array with a fixed size of 4 elements, found one with 7 elements

Note the FourCC value may contain non-printable byte values, including the byte-value zero.

Debug display

let uuid = FourCC(*b"uuid");
println!("it's {:?}", uuid);  // produces: it's FourCC{uuid}

Note that if the FourCC bytes are not able to be converted to UTF8, then a fallback representation will be used (as it would be suprising for format!() to panic).

let uuid = FourCC(*b"u\xFFi\0");
println!("it's {:?}", uuid);  // produces: it's FourCC{u\xffi\x00}

Structs

• FourCC
  A four-character-code value.