Macro const_format::call_debug_fmt

source · [−]

macro_rules! call_debug_fmt {
    (array, $expr:expr, $formatter:expr $(,)* ) => { ... };
    (slice, $expr:expr, $formatter:expr $(,)*) => { ... };
    (Option, $expr:expr, $formatter:expr $(,)*) => { ... };
    (newtype $name:ident, $expr:expr, $formatter:expr $(,)*) => { ... };
    (std, $expr:expr, $formatter:expr $(,)*) => { ... };
    (other, $expr:expr, $formatter:expr $(,)*) => { ... };
}

Available on crate feature fmt only.

Expand description

For debug formatting of some specific generic std types, and other types.

Errors

This macro propagates errors from the debug formatting methods that it calls, by returning them.

Macro variants

The macro has these variants:

slice (also array): to format a slice or an array of *any debug type.
Option: to format an Option of *any debug type.
newtype: to format a single field tuple struct (eg: struct Foo(Bar);) which wraps *any debug type.
std: to format the standard library types, where PWrapper<ThatType> has a const_debug_fmt method.
other: to format non-standard-library types that have a const_debug_fmt method.

*“any debug type” meaning types that have a const_debug_fmt method

Example

Printing all of them

Printing all of the kinds of types this supports.

#![feature(const_mut_refs)]

use const_format::{
    for_examples::{Point3, Unit},
    Error, Formatter, FormattingFlags, StrWriter,
    call_debug_fmt, try_, unwrap,
};

use std::num::Wrapping;

const CAP: usize = 512;

// `call_debug_fmt` implicitly returns on error,
// so the function has to return a `Result<_, const_format::Error>`
const fn make() -> Result<StrWriter<[u8; CAP]>, Error> {
    let mut writer = StrWriter::new([0; CAP]);
    let mut fmt = Formatter::from_sw(&mut writer, FormattingFlags::NEW);
    let mut fmt = fmt.debug_struct("Foo");

    let point = Point3{ x: 5, y: 8, z: 13 };

    call_debug_fmt!(array, [Unit, Unit], fmt.field("array") );
    call_debug_fmt!(slice, [0u8, 1], fmt.field("slice") );
    call_debug_fmt!(Option, Some(point), fmt.field("option") );
    call_debug_fmt!(newtype NumWrapping, Wrapping(255u16), fmt.field("newtype") );
    call_debug_fmt!(std, false, fmt.field("std_") );
    call_debug_fmt!(other, point, fmt.field("other") );

    try_!(fmt.finish());
    Ok(writer)
}

const TEXT: &str = {
    const PROM: &StrWriter<[u8]> = &unwrap!(make());
    PROM.as_str_alt()
};

const EXPECTED: &str = "\
    Foo { \
        array: [Unit, Unit], \
        slice: [0, 1], \
        option: Some(Point3 { x: 5, y: 8, z: 13 }), \
        newtype: NumWrapping(255), \
        std_: false, \
        other: Point3 { x: 5, y: 8, z: 13 } \
    }\
";

assert_eq!(TEXT, EXPECTED);

Used as `formatc` argument

This macro can be used in the formatting macros by using the Formatter in the argument,
with the |formatter_ident| expression_that_uses_formatter syntax.