Add a std::io::read_to_string function

[camelid]

I recognize that you're usually supposed to open an issue first, but the
implementation is very small so it's okay if this is closed and it was 'wasted
work' :)

---

The equivalent of std::fs::read_to_string, but generalized to all
Read impls.

As the documentation on std::io::read_to_string says, the advantage of
this function is that it means you don't have to create a variable first
and it provides more type safety since you can only get the buffer out
if there were no errors. If you use Read::read_to_string, you have to
remember to check whether the read succeeded because otherwise your
buffer will be empty.

It's friendlier to newcomers and better in most cases to use an explicit
return value instead of an out parameter.

[rust-highfive]

r? @m-ou-se

(rust-highfive has picked a reviewer for you, use r? to override)

[m-ou-se]

Thanks! Looks good!

One small comment:

[danclive]

We could add a note to the "Read::read_to_string" example to tell him that he can write such a "helper" function to help him Read a string. We don't need to add this function to the std.

[m-ou-se]

Looks good, @camelid!

@bors r+

[bors]

📌 Commit 7463292 has been approved by m-ou-se

[m-ou-se]

We could add a note to the "Read::read_to_string" example to tell him that he can write such a "helper" function to help him Read a string.

Him? Who?

We don't need to add this function to the std.

I think it's a useful addition. If people are going to write this helper function anyway, why not provide it directly?

[danclive]

@m-ou-se As you said, this function is useful sometimes. However, I was wondering what functions could be added to the standard library. These functions can also be added, right?

fn read_i32_le(reader: &mut impl Read) -> Result<i32> {
    let mut buf = [0; 4];
    reader.read_exact(&mut buf)?;
    Ok(i32::from_le_bytes(buf))
}

fn read_i64_le(reader: &mut impl Read) -> Result<i64> {
    let mut buf = [0; 8];
    reader.read_exact(&mut buf)?;
    Ok(i64::from_le_bytes(buf))
}

...

[lnicola]

This seems like a good roll-up candidate.

EDIT: sorry, never mind, I didn't notice the PRs doing exactly that.