Question about (de)serializing vectors

[corvusrabus]

Hi, thanks for providing this great crate.
Currently, when I am using the crate to serialise a vector inside a struct it will be flattened, so say I have:

struct A {
a : String,
b : Vec<i64>
}

and I have a flexible writer, then two As {"Hello",[1,2,3]}, {"Bye", [4,5,6,7]} would be serialized to
"Hello", 1,2,3,
"Bye", 4,5,6,7

Is there any way I can tell the CSV writer to serialize it to
"Hello", [1,2,3]
"Bye", [4,5,6,7]
?

[BurntSushi]

Please provide a complete Rust program, any relevant inputs, actual output and desired output.

[corvusrabus]

Program

use std::io;
use serde::{Serialize, Deserialize};

#[derive(Serialize, Deserialize, Debug)]
struct A {
a: String,
b: Vec,
}

fn main() {
let x = A { a: "Hello".to_string(), b: vec![1, 2, 3] };
let y = A { a: "Bye".to_string(), b: vec![4, 5, 6, 7] };
let mut w = csv::WriterBuilder::new()
.flexible(true).has_headers(false).from_writer(io::stdout());
w.serialize(x);
w.serialize(y);
}

Actual output
Hello,1,2,3
Bye,4,5,6,7
Desired output
Hello,[1,2,3]
Bye,[4,5,6,7]

[ammernico]

Hi, I have the same problem. But I guess the behavior is known since it's documented here:
Nested containers are flattened to their scalar components
https://docs.rs/csv/1.3.0/csv/struct.Writer.html#non-struct-containers

Is this behavior desired? It seems an odd choice for serializing into csv

[BurntSushi]

It's not only desired, I'm not aware of any reasonable alternative other than disallowing it entirely. If you call it odd, why not say why it's odd and suggest an alternative behavior?

The OP's suggestion is not reasonable here because it layers a completely different serialization format that is not CSV on top of CSV.