`[T]` cannot be formatted with the default formatter - rust

Question

I am learning Rust through a educationnal project, where I wish to implement mathematical Matrices and Vectors. I am doing this for the sake of learning Rust.
I am having an issue displaying a slice of generic type in my Display function.
Here my Vector.rs file is as such:
use std::fmt;
#[derive(Debug)]
struct Vector<'a, K> {
data: &'a [K]
}
impl<'a, K> Vector<'a, K> {
fn new(data: &'a [K]) -> Vector<'a, K> {
Vector {
data: data
}
}
fn len(&self) -> usize {
self.data.len()
}
}
impl<'a, K> fmt::Display for Vector<'a, K>
where K: std::fmt::Display {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
write!(f, "{}", self.data)
}
}
fn main() {
println!("Test File for Vectors");
let mut v = [0.1, 0.2, 0.3, 0.4];
let my_v = Vector::new(&v);
}
When Compiling, I face the following error
error[E0277]: `[K]` doesn't implement `std::fmt::Display`
--> Vector.rs:22:19
|
22 | write!(f, "{}", self.data)
| ^^^^^^^^^ `[K]` cannot be formatted with the default formatter
|
This error is saying I need to implement Display for the type [K] which I do not understand.
Here my type K is f64 so the Display does exists, and I also added the line where K: std::fmt::Display to be certain that type K has the Display function.
Is what I am trying to do impossible ? Did I missunderstand slices ?
Thank you.

Answer 1

Display is meant for the endusers, Debug is meant for the developers.
Usually, messages to endusers don't include representations of vectors, so Vec/Slice does not implement Display. They are only printable via Debug.
As your struct is actually meant to be displayed to the enduser, you need to implement Display for it yourself by actually serializing every element and then joining and formatting them the way you like.
For example, like this:
use std::fmt;
#[derive(Debug)]
struct Vector<'a, K> {
data: &'a [K],
}
impl<'a, K> Vector<'a, K> {
fn new(data: &'a [K]) -> Vector<'a, K> {
Vector { data: data }
}
}
impl<'a, K> fmt::Display for Vector<'a, K>
where
K: std::fmt::Display,
{
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
let formatted_elements = self
.data
.iter()
.map(|el| format!("{}", el))
.collect::<Vec<_>>();
let elements = formatted_elements.join(", ");
write!(f, "[{}]", elements)
}
}
fn main() {
let v = [0.1, 0.2, 0.3, 0.4];
let my_v = Vector::new(&v);
println!("{}", my_v);
}
[0.1, 0.2, 0.3, 0.4]