2 unstable releases

0.2.0 Aug 18, 2022
0.1.0 Aug 17, 2022

#624 in Debugging

MIT license

135 lines


Use the Display trait if it's satisfied, fallback to Debug otherwise, and if neither are implemented use a default string value.


The typical "nice" way to display things is via the Display trait. However, sometimes this trait is not available, but Debug is. Debug is easy to derive. In those cases it would be nice to use Debug as a fallback.


use visual::{vis, Visual};

fn main() {
    // The `vis!` macro wraps your type in such a way that it can decide which trait to
    // use: `Display`, `Debug` or neither
    printer(vis!("hello"));       // `&str` implements `Display`, so use it
    printer(vis!(vec![1, 2, 3])); // `Vec` does not, but it impls `Debug`, so we use that

    struct MyStruct;
    printer(vis!(MyStruct));      // `MyStruct` impls neither, so we use a default string value

fn printer<T>(t: Visual<T>) {        // Use the `Visual` wrapper around your type
    println!("{}", t.get_display()); // Use `get_display` to get a string representation of your type

If neither trait is implemented, the string representation will be the one defined by visual::get_non_displayable_string(). This default label can be initialized to a custom value once, by calling visual::set_non_displayable_string("value").


For the magic to work, I use the "autoderef hack" proposed by Lukas Kalbertodt, which in turn is based on David Tolnay's technique.

No runtime deps