Tracking issue for Option::deref, Result::deref, Result::deref_ok, and Result::deref_err (feature: inner_deref)

[U007D]

API

impl<T, E> Result<T, E> {
    fn as_deref(&self) -> Result<&T::Target, &E> where T: Deref;
    fn as_deref_err(&self) -> Result<&T, &E::Target> where E: Deref;
    fn as_deref_mut(&mut self) -> Result<&mut T::Target, &mut E> where T: DerefMut;
    fn as_deref_mut_err(&mut self) -> Result<&mut T, &mut E::Target> where E: DerefMut;
}

Implementation history

• Implemented in Implement inner deref for Option and Result #50267 as:

  impl<T> Option<T> {
      fn deref(&self) -> Option<&T::Target> where T: Deref;
  }
  impl<T, E> Result<T, E> {
      fn deref(&self) -> Result<&T::Target, &E::Target> where T: Deref, E: Deref;
      fn deref_ok(&self) -> Result<&T::Target, &E> where T: Deref;
      fn deref_err(&self) -> Result<&T, &E::Target> where E: Deref;
  }

• Renamed and extended in as_deref() and as_deref_mut() impls #59628 / Introduce as_deref to Option #62421:

  impl<T> Option<T> {
      fn as_deref(&self) -> Option<&T::Target> where T: Deref;
      fn as_deref_mut(&mut self) -> Option<&mut T::Target> where T: DerefMut;
  }
  impl<T, E> Result<T, E> {
      fn as_deref(&self) -> Result<&T::Target, &E::Target> where T: Deref, E: Deref;
      fn as_deref_ok(&self) -> Result<&T::Target, &E> where T: Deref;
      fn as_deref_err(&self) -> Result<&T, &E::Target> where E: Deref;
      fn as_deref_mut(&mut self) -> Result<&mut T::Target, &mut E::Target> where T: DerefMut, E: DerefMut;
      fn as_deref_mut_ok(&mut self) -> Result<&mut T::Target, &mut E> where T: DerefMut;
      fn as_deref_mut_err(&mut self) -> Result<&mut T, &mut E::Target> where E: DerefMut;
  }

• Option methods stabilized in Stabilize Option::as_deref and Option::as_deref_mut #64708:

  impl<T> Option<T> {
      fn as_deref(&self) -> Option<&T::Target> where T: Deref;
      fn as_deref_mut(&mut self) -> Option<&mut T::Target> where T: DerefMut;
  }

• Result methods pared down and renamed in Rename Result::as_deref_ok to as_deref #67930:

  impl<T, E> Result<T, E> {
      fn as_deref(&self) -> Result<&T::Target, &E> where T: Deref;
      fn as_deref_err(&self) -> Result<&T, &E::Target> where E: Deref;
      fn as_deref_mut(&mut self) -> Result<&mut T::Target, &mut E> where T: DerefMut;
      fn as_deref_mut_err(&mut self) -> Result<&mut T, &mut E::Target> where E: DerefMut;
  }

[U007D]

closed prematurely

[RalfJung]

I just found this useful! Thanks @Centril for pointing me here. :)

However, the name is a bit odd: It goes from &Option<T> to Option<T::Target>, e.g. from &Option<String> to Option<&str> -- that's just as much taking a reference as dereferencing one.

[U007D]

Ah, naming... :)

[oxalica]

Oh, the method name collides Deref::deref, quite misleading.

I think as_deref could be better name.

[197g]

What about the name deref_inner for the case of Option and both arguments of Result; although the more though I put into it the more as_deref seems correct? Compared to other ref-utils this is missing the mut variants such as deref_ok_mut. I have mixed feelings about the api as a whole though, is there enough expressiveness advantage over a plain result.as_ref().map(|t| &**t)?