The voncount from npmccallum

voncount's Introduction

Welcome to voncount - a Rust crate for counters.

Like the lovable Count von Count from Sesame Street, the voncount crate loves to count things. We provide the Counter trait which can be implemented on types which try to count things. We also provide two structs which implement the Counter trait:

ReadCounter
WriteCounter

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Provide an example

I tried to use this crate, but struggled a lot because I couldn't get my code to work:

martin.mein-iserv.de ~/git/rust/bufreader (master) # cat src/main.rs 
use std::fs::File;
use std::io::BufReader;
use std::io::Error;
use std::io::BufRead;
use voncount::ReadCounter;
use voncount::Counter;

fn main() -> Result<(), Error>{
    let fh = File::open("test.txt")?;
    let readcounter = ReadCounter::from(fh);
    let reader = BufReader::new(readcounter);

    for line in reader.lines()
    {
        println!("line: {:?}", line);
    }

    println!("read bytes: {}", readcounter.count());

    Ok(())
}

And the error message wasn't particularly helpful:

martin.mein-iserv.de ~/git/rust/bufreader (master) # cargo run      
   Compiling bufreader v0.1.0 (/root/git/rust/bufreader)
error[E0277]: the trait bound `ReadCounter<'_, _>: From<File>` is not satisfied
  --> src/main.rs:10:23
   |
10 |     let readcounter = ReadCounter::from(fh);
   |                       ^^^^^^^^^^^ the trait `From<File>` is not implemented for `ReadCounter<'_, _>`
   |
   = help: the trait `From<&mut _>` is implemented for `ReadCounter<'_, _>`
   = help: for that trait implementation, expected `&mut _`, found `File`

For more information about this error, try `rustc --explain E0277`.
error: could not compile `bufreader` (bin "bufreader") due to 1 previous error

After a while, I finally figured it out - I need to pass mutable references to ReadCounter and BufReader:

martin.mein-iserv.de ~/git/rust/bufreader (master) # cat src/main.rs
use std::fs::File;
use std::io::BufReader;
use std::io::Error;
use std::io::BufRead;
use voncount::ReadCounter;
use voncount::Counter;

fn main() -> Result<(), Error>{
    let mut fh = File::open("test.txt")?;
    let mut readcounter = ReadCounter::from(&mut fh);
    let reader = BufReader::new(&mut readcounter);

    for line in reader.lines()
    {
        println!("line: {:?}", line);
    }

    println!("read bytes: {}", readcounter.count());

    Ok(())
}

martin.mein-iserv.de ~/git/rust/bufreader (master) # cargo run      
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.00s
     Running `target/debug/bufreader`
line: Ok("hello")
line: Ok("world")
read bytes: 12

This example might be helpful to others, so I'm posting it here.

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