[−][src]Crate const_format

Macros for concatenating and formatting constants into &'static str constants.

Examples

Concatenation

use const_format::concatcp;

const NAME: &str = "Bob";
const FOO: &str = concatcp!(NAME, ", age ", 21u8,"!");

assert_eq!(FOO, "Bob, age 21!");

Formatting

use const_format::formatcp;

const NAME: &str = "John";

const FOO: &str = formatcp!("{NAME}, age {}!", compute_age(NAME));

assert_eq!(FOO, "John, age 24!");

Limitations

All of the macros from const_format have these limitations:

  • They cannot take constants that use generic parameters, so while Type::<u8>::FOO is fine Type::<T>::FOO is not (T being a type parameter).

  • Integer arguments must have a type inferrable from context, more details in the Integer arguments section.

  • They cannot be used places that take string literals. So #[doc = "foobar"] cannot be replaced with #[doc = concatcp!("foo", "bar") ].

Integer arguments

Integer arguments must have a type inferrable from context. so if you only pass an integer literal it must have a suffix.

Example of what does compile:

const N: u32 = 1;
assert_eq!(const_format::concatcp!(N + 1, 2 + N), "23");

assert_eq!(const_format::concatcp!(2u32, 2 + 1u8, 3u8 + 1), "234");

Example of what does not compile:

ⓘThis example deliberately fails to compile
assert_eq!(const_format::concatcp!(1 + 1, 2 + 1), "23");

Cargo features

None yet.

No-std support

const_format is unconditionally #![no_std], so it can be used anywhere Rust can be used.

Minimum Supported Rust Version

const_format requires Rust 1.46.0, because it uses looping an branching in const contexts.

Features that require versions of Rust, or the nightly compiler, need to be explicitly enabled with cargo features.

Macros

concatcp

Concatenates constants of primitive types into a &'static str.

formatcp

Formats constants of primitive types into a &'static str