Function default_read_to_string 

#[doc(hidden)]
pub(crate) fn default_read_to_string<R>(
    r: &mut R,
    buf: &mut String,
    size_hint: Option<usize>,
) -> Result<usize, Error>
where
    R: Read + ?Sized,

🔬This is a nightly-only experimental API. (core_io_internals)