How to build WriteBuf from array - buffer

Question

I am serializing two values in to an array and I am trying to go through a WriteBuf but I am getting the error that
error: the trait `std::io::Write` is not implemented for the type `[_; 12]`
error: type `std::io::buffered::BufWriter<&mut [_; 12]>` does not implement any method in scope named `write_be_u32`
error: type `std::io::buffered::BufWriter<&mut [_; 12]>` does not implement any method in scope named `write_be_f64`
Here is the minimum code to generate this error:
use std::io::{ BufWriter, Write };
fn main(){
let packed_data = [0; 12];
let timestamp : u32 = 100;
let value : f64 = 9.9;
let writer = BufWriter::new(&mut packed_data);
writer.write_be_u32(timestamp);
writer.write_be_f64(value);
println!("Packed data looks like {:?}", packed_data);
}
Am I no borrowing the slice correctly? Am I note using the proper module to define the Write trait for my buffer?
Here is a playpen for this code: http://is.gd/ol8qND

Answer 1

I see a few potential problems with your code:
packed_data isn't mutable.
You use packed_data at the end of main while writer holds a mutable reference to it.
I don't think that either of those things are causing the error. I did however find something that works:
use std::io::{ BufWriter, Write };
fn main() {
let mut packed_data = [0; 12];
{
let packed_data_ref: &mut [u8] = &mut packed_data;
let mut writer = BufWriter::new(packed_data_ref);
writer.write(&[1, 2, 3, 4]).unwrap();
} // `writer` gets deallocated and releases the mutable reference
println!("Packed data looks like {:?}", packed_data);
}
[playpen]
So I guess the issue is that you need a &[u8] rather than a &[u8; 12]. I have no idea why. I hope this at least helps though.