fmt::Debug hardly looks compact and clean, so it is often advantageous to customize the output appearance. This is done by manually implementing fmt::Display, which uses the {} print marker. Implementing it looks like this:
>#![allow(unused)]
>fn main() {
>// Import (via `use`) the `fmt` module to make it available.
>use std::fmt;
>// Define a structure for which `fmt::Display` will be implemented. This is
>// a tuple struct named `Structure` that contains an `i32`.
>struct Structure(i32);
>// To use the `{}` marker, the trait `fmt::Display` must be implemented
>// manually for the type.
>impl fmt::Display for Structure {
>// This trait requires `fmt` with this exact signature.
>fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
>// Write strictly the first element into the supplied output
>// stream: `f`. Returns `fmt::Result` which indicates whether the
>// operation succeeded or failed. Note that `write!` uses syntax which
>// is very similar to `println!`.
>write!(f, "{}", self.0)
>}
>}
>}
fmt::Display may be cleaner than fmt::Debug but this presents a problem for the std library. How should ambiguous types be displayed? For example, if the std library implemented a single style for all Vec, what style should it be? Would it be either of these two?
• Vec: /:/etc:/home/username:/bin (split on :)
• Vec: 1,2,3 (split on ,)
No, because there is no ideal style for all types and the std library doesn't presume to dictate one. fmt::Display is not implemented for Vec or for any other generic containers. fmt::Debug must then be used for these generic cases.
This is not a problem though because for any new container type which is not generic,fmt::Display can be implemented.
>use std::fmt; // Import `fmt`
>// A structure holding two numbers. `Debug` will be derived so the results can
>// be contrasted with `Display`.
>#[derive(Debug)]
>struct MinMax(i64, i64);
>// Implement `Display` for `MinMax`.
>impl fmt::Display for MinMax {
>fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
>// Use `self.number` to refer to each positional data point.
