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Implement TryFrom for CString and CStr #44916

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Implement TryFrom for CString and CStr #44916

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28 changes: 28 additions & 0 deletions src/libstd/ffi/c_str.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,7 @@
use ascii;
use borrow::{Cow, Borrow};
use cmp::Ordering;
use convert::TryFrom;
use error::Error;
use fmt::{self, Write};
use io;
Expand Down Expand Up @@ -646,6 +647,24 @@ impl From<CString> for Vec<u8> {
}
}

#[unstable(feature = "try_from", issue = "33417")]
impl TryFrom<Vec<u8>> for CString {
type Error = NulError;

fn try_from(bytes: Vec<u8>) -> Result<CString, NulError> {
CString::_new(bytes)
}
}

#[unstable(feature = "try_from", issue = "33417")]
impl TryFrom<CString> for String {
type Error = IntoStringError;

fn try_from(c_str: CString) -> Result<String, IntoStringError> {
c_str.into_string()
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This checks for valid UTF-8 so this impl should also be removed.

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TryFrom<CString> for String is an obvious conversion. The underlying conversion checks valid UTF-8 but CString is a named and obvious type unlike Vec<u8>.

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A CString is a sequence of none nul bytes. A Vec<u8> is a sequence of bytes. The conversion to String is exactly the same so it doesn't make sense to include one but not the other.

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@kennytm @sfackler do you guys have any input on this?

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I'd lean towards leaving this out for now.

}
}

#[stable(feature = "cstr_debug", since = "1.3.0")]
impl fmt::Debug for CStr {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
Expand All @@ -657,6 +676,15 @@ impl fmt::Debug for CStr {
}
}

#[unstable(feature = "try_from", issue = "33417")]
impl<'a> TryFrom<&'a [u8]> for &'a CStr {
type Error = FromBytesWithNulError;

fn try_from(bytes: &[u8]) -> Result<&CStr, FromBytesWithNulError> {
CStr::from_bytes_with_nul(bytes)
}
}

#[stable(feature = "cstr_default", since = "1.10.0")]
impl<'a> Default for &'a CStr {
fn default() -> &'a CStr {
Expand Down