ACP: Add FromByteStr trait with blanket impl FromStr · Issue #287 · rust-lang/libs-team (original) (raw)

Proposal

Problem statement

Many data forms that can be parsed from a string representation do not need UTF-8. Here, FromStr is unnecessarily restrictive because a byte slice &[u8] cannot be parsed directly. Instead, a UTF-8 &str must be constructed to use .parse().

This is inconvenient when working with any raw buffers where one cannot assume that str::from_utf8 will be successful, nor is there any reason to incur the UTF-8 verification overhead. An example is IP addresses, for which there is an unstable from_bytes function: rust-lang/rust#101035

Motivating examples or use cases

Any input data where UTF-8 cannot be guaranteed: stdin, file paths, data from Read, network packets, no_std without UTF tables, any data read one byte at a time, etc.

Any output data that doesn't require specific knowledge of UTF-8: integers, floating point, IP/socket addresses, MAC addresses, UUIDs, etc.

Solution sketch

Add a trait that mirrors FromStr but works with &[u8] byte slices:

// Likely located in core::slice pub trait FromByteStr: Sized { type Err;

// Required method
fn from_byte_str(bytes: &[u8]) -> Result<Self, Self::Err>;

}

This will get a corresponding parse on &[u8]

impl<[u8]> { pub fn parse(&self) -> Result<F, ::Err> where F: FromByteStr { /* ... */ } }

Since &str is necessarily represented as &[u8], we can provide a blanket impl so no types need to be duplicated:

impl FromStr for T where T: FromByteStr { type Err = T::Err; fn from_str(s: &str) -> Result<Self, Self::Err> { s.as_bytes().parse() } }

If this is done, almost all types in std that implement FromStr will be able to switch to a FromByteStr implementation:

Alternatives

Open Questions

What happens now?

This issue contains an API change proposal (or ACP) and is part of the libs-api team feature lifecycle. Once this issue is filed, the libs-api team will review open proposals as capability becomes available. Current response times do not have a clear estimate, but may be up to several months.

Possible responses

The libs team may respond in various different ways. First, the team will consider the problem (this doesn't require any concrete solution or alternatives to have been proposed):

Second, if there's a concrete solution: