How do I pass a Vec> to a function?

Question

Given a 2D vector of i32s:

let v = vec![
    vec![1, 1, 1], 
    vec![0, 1, 0], 
    vec![0, 1, 0],
];

How can I pass it to a function to ultimately print its details? I tried:

fn printVector(vector: &[[i32]]) {
    println!("Length{}", vector.len())
}

Check this question https://stackoverflow.com/questions/13102786/two-dimensional-vectors-in-rust — ozkriff, Aug 15 '18 at 13:08
Idiomatic Rust uses `snake_case` for variables, methods, macros, and fields; `UpperCamelCase` for types; and `SCREAMING_SNAKE_CASE` for statics and constants. Use `print_vector` instead, please. — Shepmaster, Aug 15 '18 at 13:20
See also [What type should I use for a 2-dimensional array?](https://stackoverflow.com/q/29523895/155423); [Creating a Vector of Vectors in Rust](https://stackoverflow.com/q/35630131/155423); [How can you easily borrow a Vec> as a &[&[T\]\]?](https://stackoverflow.com/q/50056778/155423). — Shepmaster, Aug 15 '18 at 13:59
How do you want to pass `v` to the function? As value? As [reference](https://doc.rust-lang.org/std/primitive.reference.html)? Do you need the function to handle `Vec` or is a [slice](https://doc.rust-lang.org/std/slice/) enough? See *[What is the difference between passing a value to a function by reference and passing it by Box?](https://stackoverflow.com/questions/27305585)* — Tim Diekmann, Aug 15 '18 at 14:14
It has nothing to do with offending eyes or something. This is the warning from the rust compiler: *warning: function `printVector` should have a snake case name such as `print_vector`* — Tim Diekmann, Aug 15 '18 at 14:31
I'm aware of the compiler warnings. It's just a silly thing to complain about. Lots of helpful people gave me actual solutions rather than nit pick the question syntax. Those are the people who actually make stackover flow worth using. — camccar, Aug 15 '18 at 15:48
Possible duplicate of [How can you easily borrow a Vec> as a &\[&\[T\]\]?](https://stackoverflow.com/questions/50056778/how-can-you-easily-borrow-a-vecvect-as-a-t) — mcarton, Aug 15 '18 at 16:44
@camccar After his comment on the syntax, Shepmaster did your job and researched similar questions, and then gave you links to 3 different relevant questions. Those are the people who actually make stackoverflow worth using. — mcarton, Aug 15 '18 at 16:49

Tim Diekmann · Answer 1 · 2018-08-15T14:54:40.773

You may use a function which accepts a slice of T where T can also be referenced as a slice:

fn print_vector<T>(value: &[T])
where
    T: AsRef<[i32]>,
{
    for slice in value {
        println!("{:?}", slice.as_ref())
    }
}

playground

If you want to accept any type instead of just i32, you can also generalize this:

fn print_vector<T, D>(value: &[T])
where
    T: AsRef<[D]>,
    D: Debug,
{
    for slice in value {
        println!("{:?}", slice.as_ref())
    }
}

playground

score 5 · Answer 2 · edited Aug 15 '18 at 13:25

5

Since you're going to pass vectors to your function, the following code should work:

fn print_vector(vector: Vec<Vec<i32>>) {
    println!("Length{}", vector.len())
}

edited Aug 15 '18 at 13:25

Shepmaster

388,571
95
1,107
1,366

answered Aug 15 '18 at 13:10

Igor Drozdov

14,690
5
37
53

3

This is the only answer which accepts a `Vec` as an argument, not a reference to one. – Shepmaster Aug 15 '18 at 13:56

score 3 · Answer 3 · answered Aug 15 '18 at 13:11

You need to pass a slice of vectors - &[Vec<i32>], not a slice of slices:

fn print_vector(vector: &[Vec<i32>]) {
    println!("Length {}", vector.len())
}

fn main() {
    let v = vec![vec![1, 1, 1], vec![0, 1, 0], vec![0, 1, 0]];
    print_vector(&v);
}

Playground

score 1 · Accepted Answer · edited Aug 15 '18 at 14:38

fn printVector(vector: &Vec<Vec<i32>>) {
    println!("Length{}", vector.len())
}

let v = vec![
    vec![1, 1, 1],
    vec![0, 1, 0],
    vec![0, 1, 0],
];
printVector(&v);

In this example, &Vec<Vec<i32> and &[Vec<i32>] are no different; maybe you want to change to this:

fn print_vector(vector: &[Vec<i32>]) {
    for i in vector {
        for j in i {
            println!("{}", j)
        }
    }
}

let v = vec![
    vec![1, 1, 1],
    vec![0, 1, 0],
    vec![0, 1, 0],
];
print_vector(&v);

How do I pass a Vec> to a function?

4 Answers4