Pushing array values to a vector in Rust

Question

The Rust Programming Language has a task to print The Twelve Days of Christmas taking advantage of its repetitiveness.

My idea was to gather all the presents in an array and push them to the vector which would be printed from iteration to iteration.

It seems that it's either impossible, not easy, or I don't get something.

The code:

fn main() {
    let presents = [
        "A song and a Christmas tree",
        "Two candy canes",
        "Three boughs of holly",
    ];

    let mut current_presents = Vec::new();

    for day in presents {
        current_presents.push(presents[day]);
        println!(
            "On the {} day of Christmas my good friends brought to me",
            day + 1
        );
        println!("{current_presents} /n");
    }
}

error[E0277]: the type `[&str]` cannot be indexed by `&str`
  --> src/main.rs:11:31
   |
11 |         current_presents.push(presents[day]);
   |                               ^^^^^^^^^^^^^ slice indices are of type `usize` or ranges of `usize`
   |
   = help: the trait `SliceIndex<[&str]>` is not implemented for `&str`
   = note: required because of the requirements on the impl of `Index<&str>` for `[&str]`

error[E0369]: cannot add `{integer}` to `&str`
  --> src/main.rs:14:17
   |
14 |             day + 1
   |             --- ^ - {integer}
   |             |
   |             &str

error[E0277]: `Vec<_>` doesn't implement `std::fmt::Display`
  --> src/main.rs:16:20
   |
16 |         println!("{current_presents} /n");
   |                    ^^^^^^^^^^^^^^^^ `Vec<_>` cannot be formatted with the default formatter
   |
   = help: the trait `std::fmt::Display` is not implemented for `Vec<_>`
   = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
   = note: this error originates in the macro `$crate::format_args_nl` (in Nightly builds, run with -Z macro-backtrace for more info)

Please help me debug or push me in the right direction that wouldn't be typing down 12 separate strings and printing them 1 by 1.

hkBst · Accepted Answer · 2023-04-03 13:33:13Z

3

This works:

fn main() {
    let presents = [
        "A song and a Christmas tree",
        "Two candy canes",
        "Three boughs of holly",
    ];

    let mut current_presents = Vec::new();

    for (day, present) in presents.iter().enumerate() {
        current_presents.push(present);
        println!(
            "On the {} day of Christmas my good friends brought to me",
            day + 1
        );
        println!("{current_presents:?}\n");
    }
}

edited Apr 3, 2023 at 13:33

answered May 8, 2022 at 18:25

hkBst

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5 Comments

Swantewit Over a year ago

Thank you very much! Is there perhaps a leaner approach to get a similar effect in this language?

kmdreko Over a year ago

@Swantewit do you mean iterating by index like it seems you wanted to do in your question? You would do for day in 0..presents.len()

will Over a year ago

I am a little dissapointed that there isn't some kind function in Vector to load from an array or something generic like a (abstract) collection. Am I off-track?

hkBst Over a year ago

@will, I believe in this instance the Vec is supposed to grow by one item each iteration to match the well-known verse.

will Over a year ago

Yes, I see now. My mistake.

Shepmaster · Accepted Answer · 2022-05-09 17:53:24Z

0

The final answer looks like this (you can add all the verses up to 12th):

fn main() {
    let presents = [
        "A song and a Christmas tree",
        "Two candy canes",
        "Three boughs of holly",
        "Four coloured lights",
    ];

    for (day, _) in presents.iter().enumerate() {
        let mut presents = presents;

        let current_presents = &mut presents[0..day + 1];

        println!(
            "On the {} day of Christmas my good friends brought to me",
            day + 1
        );

        current_presents.reverse();

        current_presents
            .iter()
            .for_each(|present| print!("{} \n", present));
        println!("\n")
    }
}

edited May 9, 2022 at 17:53

Shepmaster

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answered May 9, 2022 at 17:46

Swantewit

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Comments

will · Accepted Answer · 2023-04-01 12:35:27Z

0

I suspect I've found a satisfying answer for my dissapointment:

 let a = [10, 20, 30, 40]; // a plain array
 let v = a.to_vec();

See manual:

Primitive Type slice

Credits to coder wall:

Convert a slice or an array to a Vec in Rust

answered Apr 1, 2023 at 12:35

will

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