Format slices / arrays

The {=[?]} parameter can be used to log a slice of values that implement the Format trait.

The expected argument is a slice.

#![allow(unused)]
fn main() {
extern crate defmt;
use defmt::Format;

#[derive(Format)]
struct X {
    y: u16,
    z: u8,
}

let xs: &[X] = &[ /* .. */ ];
defmt::info!("xs={=[?]}", xs);
}

[T] where T: Format also implements the Format trait so it’s possible to format [T] with {=?} but {=[?]} uses slightly less bandwidth.

💡 Note that for slices of bytes, {=[u8]} should be preferred as it’s better compressed.

Arrays

If you have an array of types that implement the Format trait, you should use the {=[?; N]} parameter (where N is the number of elements); this saves bandwidth compared to {=[?]}.

#![allow(unused)]
fn main() {
extern crate defmt;
use defmt::Format;

#[derive(Format)]
struct X {
    y: u16,
    z: u8,
}

let xs: [X; 2] = [
    X { y: 1, z: 2 },
    X { y: 3, z: 4 },
    // ..
];
defmt::info!("xs={=[?; 2]}", xs);
}