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derive(Display) /// `From<docs>`↩
===============↩
↩
[](https://crates.io/crates/displaydoc)↩
[](https://docs.rs/displaydoc)↩
↩
This library provides a convenient derive macro for the standard library's↩
[`core::fmt::Display`] trait.↩
↩
↩
```toml↩
[dependencies]↩
displaydoc = "0.2"↩
```↩
↩
*Compiler support: requires rustc 1.56+*↩
↩
<br>↩
↩
### Example↩
↩
*Demonstration alongside the [`Error`][std::error::Error] derive macro from [`thiserror`](https://docs.rs/thiserror/1.0.25/thiserror/index.html),↩
to propagate source locations from [`io::Error`][std::io::Error] with the `#[source]` attribute:*↩
```rust↩
use std::io;↩
use displaydoc::Display;↩
use thiserror::Error;↩
↩
#[derive(Display, Error, Debug)]↩
pub enum DataStoreError {↩
/// data store disconnected↩
Disconnect(#[source] io::Error),↩
/// the data for key `{0}` is not available↩
Redaction(String),↩
/// invalid header (expected {expected:?}, found {found:?})↩
InvalidHeader {↩
expected: String,↩
found: String,↩
},↩
/// unknown data store error↩
Unknown,↩
}↩
↩
let error = DataStoreError::Redaction("CLASSIFIED CONTENT".to_string());↩
assert!("the data for key `CLASSIFIED CONTENT` is not available" == &format!("{}", error));↩
```↩
*Note that although [`io::Error`][std::io::Error] implements `Display`, we do not add it to the↩
generated message for `DataStoreError::Disconnect`, since it is already made available via↩
`#[source]`. See further context on avoiding duplication in error reports at the rust blog↩
↩
<br>↩
↩
### Details↩
↩
- A `fmt::Display` impl is generated for your enum if you provide↩
a docstring comment on each variant as shown above in the example. The↩
`Display` derive macro supports a shorthand for interpolating fields from↩
the error:↩
- `/// {var}` ⟶ `write!("{}", self.var)`↩
- `/// {0}` ⟶ `write!("{}", self.0)`↩
- `/// {var:?}` ⟶ `write!("{:?}", self.var)`↩
- `/// {0:?}` ⟶ `write!("{:?}", self.0)`↩
- This also works with structs and [generic types][crate::Display#generic-type-parameters]:↩
```rust↩
/// oh no, an error: {0}↩
#[derive(Display)]↩
pub struct Error<E>(pub E);↩
↩
let error: Error<&str> = Error("muahaha i am an error");↩
assert!("oh no, an error: muahaha i am an error" == &format!("{}", error));↩
```↩
↩
- Two optional attributes can be added to your types next to the derive:↩
↩
- `#[ignore_extra_doc_attributes]` makes the macro ignore any doc↩
comment attributes (or `///` lines) after the first. Multi-line↩
comments using `///` are otherwise treated as an error, so use this↩
attribute or consider switching to block doc comments (`/** */`).↩
↩
- `#[prefix_enum_doc_attributes]` combines the doc comment message on↩
your enum itself with the messages for each variant, in the format↩
“enum: variant”. When added to an enum, the doc comment on the enum↩
becomes mandatory. When added to any other type, it has no effect.↩
↩
- In case you want to have an independent doc comment, the↩
`#[displaydoc("...")` atrribute may be used on the variant or struct to↩
override it.↩
↩
<br>↩
↩
### FAQ↩
↩
1. **Is this crate `no_std` compatible?**↩
* Yes! This crate implements the [`core::fmt::Display`] trait, not the [`std::fmt::Display`] trait, so it should work in `std` and `no_std` environments. Just add `default-features = false`.↩
↩
2. **Does this crate work with `Path` and `PathBuf` via the `Display` trait?**↩
* Yuuup. This crate uses @dtolnay's [autoref specialization technique](https://github.com/dtolnay/case-studies/blob/master/autoref-specialization/README.md) to add a special trait for types to get the display impl. It then specializes for `Path` and `PathBuf`, and when either of these types are found, it calls `self.display()` to get a `std::path::Display<'_>` type which can be used with the `Display` format specifier!↩
↩
↩
#### License↩
↩
<sup>↩
Licensed under either of <a href="LICENSE-APACHE">Apache License, Version↩
2.0</a> or <a href="LICENSE-MIT">MIT license</a> at your option.↩
</sup>↩
↩
<br>↩
↩
<sub>↩
Unless you explicitly state otherwise, any contribution intentionally submitted↩
for inclusion in this crate by you, as defined in the Apache-2.0 license, shall↩
be dual licensed as above, without any additional terms or conditions.↩
</sub>↩