Creating a struct with a generic trait for field. Expected struct found struct

Question

I\'m trying to create a struct that has a BufWriter that uses the Write trait, so that this struct could have a buffered writer that can be anythin

Answer 1

Your error is in mixing generic and specific:

impl BufWriterStruct {
    pub fn new(filename: &str) -> BufWriterStruct {
        BufWriterStruct {
            writer: Some(BufWriter::new(File::create(filename).unwrap())),
        }
    }
}

Here, your instance of BufWriter should accept a W: Write, which is decided by the caller, yet the function actually creates a File.

Let the caller decide, instead:

impl  BufWriterStruct {
    pub fn new(writer: W) -> BufWriterStruct {
        BufWriterStruct {
            writer: Some(BufWriter::new(writer)),
        }
    }
}

Of course, this will change invocation a bit:

fn main() {
    let tmp = BufWriterStruct::new(File::create("tmp.txt").unwrap());
}

And then it'll work.