derive(Display)

This library provides a convenient derive macro for the standard library's std::fmt::Display trait. displaythis is a fork of thiserror, modified for types that are not errors.

Example

# use std::io;
use displaythis::Display;

#[derive(Display, Debug)]
pub enum DataStoreError {
    #[display("data store disconnected")]
    Disconnect(io::Error),
    #[display("the data for key `{0}` is not available")]
    Redaction(String),
    #[display("invalid header (expected {expected:?}, found {found:?})")]
    InvalidHeader {
        expected: String,
        found: String,
    },
    #[display("unknown data store error")]
    Unknown,
}

Details

• displaythis deliberately does not appear in your public API. You get the same thing as if you had written an implementation of std::fmt::Display by hand, and switching from handwritten impls to displaythis or vice versa is not a breaking change.

• Types may be enums, structs with named fields, tuple structs, or unit structs.

• You should provide #[display("...")] messages on the struct or each variant of your enum, as shown above in the example.

  The messages support a shorthand for interpolating fields from the error.

  • #[display("{var}")] ⟶ write!("{}", self.var)
  • #[display("{0}")] ⟶ write!("{}", self.0)
  • #[display("{var:?}")] ⟶ write!("{:?}", self.var)
  • #[display("{0:?}")] ⟶ write!("{:?}", self.0)

  These shorthands can be used together with any additional format args, which may be arbitrary expressions. For example:

  #[derive(Display, Debug)]
  pub enum Error {
      #[display("invalid rdo_lookahead_frames {0} (expected < {})", i32::MAX)]
      InvalidLookahead(u32),
  }
  

  If one of the additional expression arguments needs to refer to a field of the struct or enum, then refer to named fields as .var and tuple fields as .0.

  #[derive(Display, Debug)]
  pub enum Error {
      #[display("first letter must be lowercase but was {:?}", first_char(.0))]
      WrongCase(String),
      #[display("invalid index {idx}, expected at least {} and at most {}", .limits.lo, .limits.hi)]
      OutOfBounds { idx: usize, limits: Limits },
  }
  

License