Debug2

debug2 is a pretty printing crate based on std::fmt

Why not just use Debug

The Debug trait is good, but the problem is it is not very good at nested stuctures. Either you use {:?} and get a line that is too long, or too many lines with not enough information on them.

let complex_structure = vec![
    vec![Some(1), Some(2), Some(3), None],
    vec![Some(2), None],
    vec![Some(4), Some(7)],
    vec![Some(1), Some(2), Some(3), None],
];
let one_line = format!("{:?}", complex_structure);
assert_eq!(one_line, "[[Some(1), Some(2), Some(3), None], [Some(2), None], [Some(4), Some(7)], [Some(1), Some(2), Some(3), None]]");
let many_lines = format!("{:#?}", complex_structure);
assert_eq!(many_lines, "[
    [
        Some(
            1,
        ),
        Some(
            2,
        ),
        Some(
            3,
        ),
        None,
    ],
    [
        Some(
            2,
        ),
        None,
    ],
    [
        Some(
            4,
        ),
        Some(
            7,
        ),
    ],
    [
        Some(
            1,
        ),
        Some(
            2,
        ),
        Some(
            3,
        ),
        None,
    ],
]")

debug2 aims to be a third alternative, that gets this correct.

use debug2::pprint;
let complex_structure = vec![
    vec![Some(1), Some(2), Some(3), None],
    vec![Some(2), None],
    vec![Some(4), Some(7)],
    vec![Some(1), Some(2), Some(3), None],
    vec![Some(2), None],
    vec![Some(4), Some(7)],
    vec![Some(1), Some(2), Some(3), None],
    vec![Some(2), None],
    vec![Some(4), Some(7)],
];
assert_eq!(
    pprint(complex_structure),
    "\
[
    [Some(1), Some(2), Some(3), None],
    [Some(2), None],
    [Some(4), Some(7)],
    [Some(1), Some(2), Some(3), None],
    [Some(2), None],
    [Some(4), Some(7)],
    [Some(1), Some(2), Some(3), None],
    [Some(2), None],
    [Some(4), Some(7)],
]"
);

debug2 provides a debug2::Debug trait, which can be derived on your types, and is implemented for common types in std.

Once your types implement debug2::Debug, you can use debug2::pprint to convert them to a string.

You can also manually implement Debug, using a subset of the API in std::fmt::Formatter

Limitations

• Speed: While doing this will always mean extra work, this crate is paticularly inefficient.
• Prevalence: Almost every type implements std::fmt::Debug, but not this type
• The derive isn't great: The derive macro for std::fmt::Debug works everywhere. This one is kind of basic, and will probably not work everywhere it should.

Prior art

• std::fmt, where much of the code comes from
• pprint from python , which showed that this sort of thing is doable and great.
• ojg, whose pretty module is the basis for this whole thing.

License