0841-read_to_string_without_buffer.md

• Feature Name: read_to_string_without_buffer
• Start Date: 2015-03-13
• RFC PR: rust-lang#970
• Rust Issue: rust-lang/rust#23335

Summary

Add read_into_string and read_into_vec methods to the Read trait that act just like read_to_string and read_to_end but don't take a buffer.

Motivation

While the fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<()> and fn read_to_string(&mut self, buf: &mut String) -> Result<()> APIs are more efficient removing the APIs that don't require passing a buffer entirely comes at with convenience loss in some situations. In particular if one want's to implement a chaining API and doesn't care about efficiency.

Today we either have to write this

fn get_last_commit () -> String {

    let output = Command::new("git")
                    .arg("rev-parse")
                    .arg("HEAD")
                    .output()
                    .ok().expect("error invoking git rev-parse");

    let encoded = String::from_utf8(output.stdout).ok().expect("error parsing output of git rev-parse");

    encoded
}

Or this:

fn get_last_commit () -> String {

    Command::new("git")
            .arg("rev-parse")
            .arg("HEAD")
            .output()
            .map(|output| {
                String::from_utf8(output.stdout).ok().expect("error reading into string")
            })
            .ok().expect("error invoking git rev-parse")
}

But we'd like to be able to just write

fn get_last_commit () -> String {

    Command::new("git")
            .arg("rev-parse")
            .arg("HEAD")
            .spawn()
            .ok().expect("error spawning process")
            .stdout.read_into_string()
            .ok().expect("error reading output")
}

This was possible before but since there is not such read_to_string API anymore, it's currently impossible.

Detailed design

Add back methods with following signature

fn read_into_vec(&mut self) -> Result<Vec<u8>>

fn read_into_string(&mut self) -> Result<String>

Drawbacks

Two more methods to maintain

Alternatives

Don't do it and force users to use things like map for chaining

Unresolved questions

None.