Macro format_description 

format_description!() { /* proc-macro */ }

Available on crate feature macros and (crate features formatting or parsing) only.

Equivalent of performing format_description::parse() at compile time.

Using the macro instead of the function results in a static slice rather than a Vec, such that it can be used in #![no_alloc] situations. For readability, you can use StaticFormatDescription as the type.

The resulting expression can be used in const or static declarations, and implements the sealed traits required for both formatting and parsing.

assert_eq!(
    format_description!("[hour]:[minute]:[second]"),
    format_description::parse("[hour]:[minute]:[second]")?
);

The syntax accepted by this macro is the same as format_description::parse(), which can be found in the book.