# parse-display
[](https://crates.io/crates/parse-display)
[](https://docs.rs/parse-display/)
[](https://github.com/frozenlib/parse-display/actions)
This crate provides derive macro `Display` and `FromStr`.
These macros use common helper attributes to specify the format.
## Install
Add this to your Cargo.toml:
```toml
[dependencies]
parse-display = "0.8.2"
```
## Example
```rust
use parse_display::{Display, FromStr};
#[derive(Display, FromStr, PartialEq, Debug)]
#[display("{a}-{b}")]
struct MyStruct {
a: u32,
b: u32,
}
assert_eq!(MyStruct { a:10, b:20 }.to_string(), "10-20");
assert_eq!("10-20".parse(), Ok(MyStruct { a:10, b:20 }));
#[derive(Display, FromStr, PartialEq, Debug)]
#[display(style = "snake_case")]
enum MyEnum {
VarA,
VarB,
}
assert_eq!(MyEnum::VarA.to_string(), "var_a");
assert_eq!("var_a".parse(), Ok(MyEnum::VarA));
```
## Helper attributes
Helper attributes can be written in the following positions.
| [`#[display("...")]`](#display) | ✔ | ✔ | ✔ | ✔ |
| [`#[display(style = "...")]`](#displaystyle--) | | ✔ | ✔ | |
| [`#[display(crate = ...)]`](#displaycrate--) | ✔ | ✔ | | |
| [`#[display(bound(...))]`](#displaybound) | ✔ | ✔ | ✔ | ✔ |
| [`#[from_str(bound(...))]`](#from_strbound) | ✔ | ✔ | ✔ | ✔ |
| [`#[from_str(regex = "...")]`](#from_strregex--) | ✔ | ✔ | ✔ | ✔ |
| [`#[from_str(new = ...)]`](#from_strnew--) | ✔ | | ✔ | |
| [`#[from_str(ignore)]`](#from_strignore) | | | ✔ | |
| [`#[from_str(default)]`](#from_strdefault) | ✔ | | | ✔ |
| [`#[from_str(default_fields(...))]`](#from_strdefault_fields) | ✔ | ✔ | ✔ | |
`#[derive(Display)]` use `#[display]`.
`#[derive(FromStr)]` use both `#[display]` and `#[from_str]`.
`key = value` style parameter can be specified only once for each key.
`key(value1, value2, ...)` style parameter can be specified multiple times.
## `#[display("...")]`
Specifies the format using a syntax similar to `std::format!()`.
However, unlike `std::format!()`, field name is specified in `{}`.
### Struct format
By writing `#[display("..")]`, you can specify the format used by `Display` and `FromStr`.
```rust
use parse_display::{Display, FromStr};
#[derive(Display, FromStr, PartialEq, Debug)]
#[display("{a}-{b}")]
struct MyStruct {
a: u32,
b: u32,
}
assert_eq!(MyStruct { a:10, b:20 }.to_string(), "10-20");
assert_eq!("10-20".parse(), Ok(MyStruct { a:10, b:20 }));
#[derive(Display, FromStr, PartialEq, Debug)]
#[display("{0}+{1}")]
struct MyTuple(u32, u32);
assert_eq!(MyTuple(10, 20).to_string(), "10+20");
assert_eq!("10+20".parse(), Ok(MyTuple(10, 20)));
```
### Newtype pattern
If the struct has only one field, the format can be omitted.
In this case, the only field is used.
```rust
use parse_display::{Display, FromStr};
#[derive(Display, FromStr, PartialEq, Debug)]
struct NewType(u32);
assert_eq!(NewType(10).to_string(), "10");
assert_eq!("10".parse(), Ok(NewType(10)));
```
### Enum format
In enum, you can specify the format for each variant.
```rust
use parse_display::{Display, FromStr};
#[derive(Display, FromStr, PartialEq, Debug)]
enum MyEnum {
#[display("aaa")]
VarA,
#[display("bbb")]
VarB,
}
assert_eq!(MyEnum::VarA.to_string(), "aaa");
assert_eq!(MyEnum::VarB.to_string(), "bbb");
assert_eq!("aaa".parse(), Ok(MyEnum::VarA));
assert_eq!("bbb".parse(), Ok(MyEnum::VarB));
```
In enum format, `{}` means variant name.
Variant name style (e.g. snake_case, camelCase, ...) can be specified by [`#[from_str(style = "...")]`](#displaystyle--).
```rust
use parse_display::{Display, FromStr};
#[derive(Display, FromStr, PartialEq, Debug)]
enum MyEnum {
#[display("aaa-{}")]
VarA,
#[display("bbb-{}")]
VarB,
}
assert_eq!(MyEnum::VarA.to_string(), "aaa-VarA");
assert_eq!(MyEnum::VarB.to_string(), "bbb-VarB");
assert_eq!("aaa-VarA".parse(), Ok(MyEnum::VarA));
assert_eq!("bbb-VarB".parse(), Ok(MyEnum::VarB));
#[derive(Display, FromStr, PartialEq, Debug)]
#[display(style = "snake_case")]
enum MyEnumSnake {
#[display("{}")]
VarA,
}
assert_eq!(MyEnumSnake::VarA.to_string(), "var_a");
assert_eq!("var_a".parse(), Ok(MyEnumSnake::VarA));
```
By writing a format on enum instead of variant, you can specify the format common to multiple variants.
```rust
use parse_display::{Display, FromStr};
#[derive(Display, FromStr, PartialEq, Debug)]
#[display("xxx-{}")]
enum MyEnum {
VarA,
VarB,
}
assert_eq!(MyEnum::VarA.to_string(), "xxx-VarA");
assert_eq!(MyEnum::VarB.to_string(), "xxx-VarB");
assert_eq!("xxx-VarA".parse(), Ok(MyEnum::VarA));
assert_eq!("xxx-VarB".parse(), Ok(MyEnum::VarB));
```
### Unit variants
If all variants has no field, format can be omitted.
In this case, variant name is used.
```rust
use parse_display::{Display, FromStr};
#[derive(Display, FromStr, PartialEq, Debug)]
enum MyEnum {
VarA,
VarB,
}
assert_eq!(MyEnum::VarA.to_string(), "VarA");
assert_eq!(MyEnum::VarB.to_string(), "VarB");
assert_eq!("VarA".parse(), Ok(MyEnum::VarA));
assert_eq!("VarB".parse(), Ok(MyEnum::VarB));
```
### Field format
You can specify the format of the field.
In field format, `{}` means the field itself.
```rust
use parse_display::{Display, FromStr};
#[derive(Display, FromStr, PartialEq, Debug)]
#[display("{a}, {b}")]
struct MyStruct {
#[display("a is {}")]
a: u32,
#[display("b is {}")]
b: u32,
}
assert_eq!(MyStruct { a:10, b:20 }.to_string(), "a is 10, b is 20");
assert_eq!("a is 10, b is 20".parse(), Ok(MyStruct { a:10, b:20 }));
#[derive(Display, FromStr, PartialEq, Debug)]
#[display("{0}, {1}")]
struct MyTuple(#[display("first is {}")] u32, #[display("next is {}")] u32);
assert_eq!(MyTuple(10, 20).to_string(), "first is 10, next is 20");
assert_eq!("first is 10, next is 20".parse(), Ok(MyTuple(10, 20)));
#[derive(Display, FromStr, PartialEq, Debug)]
enum MyEnum {
#[display("this is A {0}")]
VarA(#[display("___{}___")] u32),
}
assert_eq!(MyEnum::VarA(10).to_string(), "this is A ___10___");
assert_eq!("this is A ___10___".parse(), Ok(MyEnum::VarA(10)));
```
### Display field chain
You can use "field chain", e.g. `{x.a}` .
```rust
use parse_display::{Display, FromStr};
#[derive(PartialEq, Debug, Default)]
struct MyStruct {
a: u32,
b: u32,
}
#[derive(FromStr, Display, PartialEq, Debug)]
#[display("{x.a}")]
struct FieldChain {
#[from_str(default)]
x: MyStruct,
}
assert_eq!(FieldChain { x:MyStruct { a:10, b:20 } }.to_string(), "10");
assert_eq!("10".parse(), Ok(FieldChain { x:MyStruct { a:10, b:0 } }));
```
When using "field chain", you need to use [`#[from_str(default)]`](#from_strdefault) to implement `FromStr`.
### Format parameter
Like `std::format!()`, format parameter can be specified.
```rust
use parse_display::{Display, FromStr};
#[derive(Display, PartialEq, Debug)]
#[display("{a:>04}")]
struct WithFormatParameter {
a: u32,
}
assert_eq!(WithFormatParameter { a:5 }.to_string(), "0005");
```
## `#[display(style = "...")]`
By writing `#[display(style = "...")]`, you can specify the variant name style.
The following styles are available.
- `none`
- `lowercase`
- `UPPERCASE`
- `snake_case`
- `SNAKE_CASE`
- `camelCase`
- `CamelCase`
- `kebab-case`
- `KEBAB-CASE`
- `Title Case`
- `Title case`
- `title case`
- `TITLE CASE`
```rust
use parse_display::{Display, FromStr};
#[derive(Display, FromStr, PartialEq, Debug)]
#[display(style = "snake_case")]
enum MyEnum {
VarA,
VarB,
}
assert_eq!(MyEnum::VarA.to_string(), "var_a");
assert_eq!("var_a".parse(), Ok(MyEnum::VarA));
#[derive(Display, FromStr, PartialEq, Debug)]
enum StyleExample {
#[display(style = "none")]
VarA1,
#[display(style = "none")]
varA2,
#[display(style = "lowercase")]
VarB,
#[display(style = "UPPERCASE")]
VarC,
#[display(style = "snake_case")]
VarD,
#[display(style = "SNAKE_CASE")]
VarE,
#[display(style = "camelCase")]
VarF,
#[display(style = "CamelCase")]
VarG1,
#[display(style = "CamelCase")]
varG2,
#[display(style = "kebab-case")]
VarH,
#[display(style = "KEBAB-CASE")]
VarI,
#[display(style = "Title Case")]
VarJ,
#[display(style = "Title case")]
VarK,
#[display(style = "title case")]
VarL,
#[display(style = "TITLE CASE")]
VarM,
}
assert_eq!(StyleExample::VarA1.to_string(), "VarA1");
assert_eq!(StyleExample::varA2.to_string(), "varA2");
assert_eq!(StyleExample::VarB.to_string(), "varb");
assert_eq!(StyleExample::VarC.to_string(), "VARC");
assert_eq!(StyleExample::VarD.to_string(), "var_d");
assert_eq!(StyleExample::VarE.to_string(), "VAR_E");
assert_eq!(StyleExample::VarF.to_string(), "varF");
assert_eq!(StyleExample::VarG1.to_string(), "VarG1");
assert_eq!(StyleExample::varG2.to_string(), "VarG2");
assert_eq!(StyleExample::VarH.to_string(), "var-h");
assert_eq!(StyleExample::VarI.to_string(), "VAR-I");
assert_eq!(StyleExample::VarJ.to_string(), "Var J");
assert_eq!(StyleExample::VarK.to_string(), "Var k");
assert_eq!(StyleExample::VarL.to_string(), "var l");
assert_eq!(StyleExample::VarM.to_string(), "VAR M");
```
## `#[display(crate = ...)]`
Specify a path to the `parse-display` crate instance.
Used when `::parse_display` is not an instance of `parse-display`, such as when a macro is re-exported or used from another macro.
## `#[display(bound(...))]`
By default, the type of field used in the format is added to the trait bound.
In Rust prior to 1.59, this behavior causes a compile error if you use fields of non public type in public struct.
```rust
#![deny(private_in_public)]
use parse_display::Display;
// private type `Inner<T>` in public interface (error E0446)
#[derive(Display)]
pub struct Outer<T>(Inner<T>);
#[derive(Display)]
struct Inner<T>(T);
```
By writing `#[display(bound(...))]`, you can override the default behavior.
### Specify trait bound type
By specifying the type, you can specify the type that need to implement `Display` and `FromStr`.
```rust
use parse_display::{Display, FromStr};
#[derive(Display, FromStr, PartialEq, Debug)]
#[display(bound(T))]
pub struct Outer<T>(Inner<T>);
#[derive(Display, FromStr, PartialEq, Debug)]
struct Inner<T>(T);
assert_eq!(Outer(Inner(10)).to_string(), "10");
assert_eq!("10".parse(), Ok(Outer(Inner(10))));
```
### Specify where predicate
You can also specify the where predicate.
```rust
use parse_display::Display;
#[derive(Display)]
#[display(bound(T : std::fmt::Debug))]
pub struct Outer<T>(Inner<T>);
#[derive(Display)]
#[display("{0:?}")]
struct Inner<T>(T);
assert_eq!(Outer(Inner(10)).to_string(), "10");
```
### No trait bounds
You can also remove all trait bounds.
```rust
use parse_display::Display;
#[derive(Display)]
#[display(bound())]
pub struct Outer<T>(Inner<T>);
#[derive(Display)]
#[display("ABC")]
struct Inner<T>(T);
assert_eq!(Outer(Inner(10)).to_string(), "ABC");
```
### Default trait bounds
`..` means default (automatically generated) trait bounds.
The following example specifies `T1` as a trait bound in addition to the default trait bound `T2`.
```rust
use parse_display::Display;
pub struct Inner<T>(T);
#[derive(Display)]
#[display("{0.0}, {1}", bound(T1, ..))]
pub struct Outer<T1, T2>(Inner<T1>, T2);
assert_eq!(Outer(Inner(10), 20).to_string(), "10, 20");
```
## `#[from_str(bound(...))]`
You can use a different trait bound for `Display` and `FromStr` by specifying both `#[display(bound(...))]` and `#[from_str(bound(...))]`.
```rust
use parse_display::*;
use std::{fmt::Display, str::FromStr};
#[derive(Display, FromStr, PartialEq, Debug)]
#[display(bound("T : Display"))]
#[from_str(bound("T : FromStr"))]
pub struct Outer<T>(Inner<T>);
#[derive(Display, FromStr, PartialEq, Debug)]
struct Inner<T>(T);
assert_eq!(Outer(Inner(10)).to_string(), "10");
assert_eq!("10".parse(), Ok(Outer(Inner(10))));
```
## `#[from_str(regex = "...")]`
Specify the format of the string to be input with `FromStr`.
`#[display("...")]` is ignored, when this attribute is specified.
### Capture name
The capture name corresponds to the field name.
```rust
use parse_display::FromStr;
#[derive(FromStr, PartialEq, Debug)]
#[from_str(regex = "(?<a>[0-9]+)__(?<b>[0-9]+)")]
struct MyStruct {
a: u8,
b: u8,
}
assert_eq!("10__20".parse(), Ok(MyStruct { a:10, b:20 }));
```
### Field regex
Set `#[display("...")]` to struct and set `#[from_str(regex = "...")]` to field, regex is used in the position where field name is specified in `#[display("...")]`.
```rust
use parse_display::FromStr;
#[derive(FromStr, PartialEq, Debug)]
#[display("{a}__{b}")]
struct MyStruct {
#[from_str(regex = "[0-9]+")]
a: u8,
#[from_str(regex = "[0-9]+")]
b: u8,
}
assert_eq!("10__20".parse(), Ok(MyStruct { a:10, b:20 }));
```
If `#[from_str(regex = "...")]` is not set to field ,
it operates in the same way as when `#[from_str(regex = "(?s:.*?)")]` is set.
```rust
use parse_display::FromStr;
#[derive(FromStr, PartialEq, Debug)]
#[display("{a}{b}")]
struct MyStruct {
a: String,
b: String,
}
assert_eq!("abcdef".parse(), Ok(MyStruct { a:"".into(), b:"abcdef".into() }));
```
### Variant name
In the regex specified for enum or variant, empty name capture means variant name.
```rust
use parse_display::FromStr;
#[derive(FromStr, PartialEq, Debug)]
#[from_str(regex = "___(?<>)___")]
enum MyEnum {
VarA,
#[from_str(regex = "xxx(?<>)xxx")]
VarB,
}
assert_eq!("___VarA___".parse(), Ok(MyEnum::VarA));
assert_eq!("xxxVarBxxx".parse(), Ok(MyEnum::VarB));
```
### Regex field chain
You can use "field chain" in regex.
```rust
use parse_display::FromStr;
#[derive(PartialEq, Debug, Default)]
struct MyStruct {
a: u32,
}
#[derive(FromStr, PartialEq, Debug)]
#[from_str(regex = "___(?<x.a>[0-9]+)")]
struct FieldChain {
#[from_str(default)]
x: MyStruct,
}
assert_eq!("___10".parse(), Ok(FieldChain { x:MyStruct { a:10 } }));
```
When using "field chain", you need to use [`#[from_str(default)]`](#from_strdefault).
## `#[from_str(new = ...)]`
If `#[from_str(new = ...)]` is specified, the value will be initialized with the specified expression instead of the constructor.
The expression must return a value that implement [`IntoResult`] (e.g. `Self`, `Option<Self>`, `Result<Self, E>`).
In the expression, you can use a variable with the same name as the field name.
```rust
use parse_display::FromStr;
#[derive(FromStr, Debug, PartialEq)]
#[from_str(new = Self::new(value))]
struct MyNonZeroUSize {
value: usize,
}
impl MyNonZeroUSize {
fn new(value: usize) -> Option<Self> {
if value == 0 {
None
} else {
Some(Self { value })
}
}
}
assert_eq!("1".parse(), Ok(MyNonZeroUSize { value: 1 }));
assert_eq!("0".parse::<MyNonZeroUSize>().is_err(), true);
```
In tuple struct, variables are named with a leading underscore and their index. (e.g. `_0`, `_1`).
```rust
use parse_display::FromStr;
#[derive(FromStr, Debug, PartialEq)]
#[from_str(new = Self::new(_0))]
struct MyNonZeroUSize(usize);
impl MyNonZeroUSize {
fn new(value: usize) -> Option<Self> {
if value == 0 {
None
} else {
Some(Self(value))
}
}
}
assert_eq!("1".parse(), Ok(MyNonZeroUSize(1)));
assert_eq!("0".parse::<MyNonZeroUSize>().is_err(), true);
```
## `#[from_str(ignore)]`
Specifying this attribute for a variant will not generate `FromStr` implementation for that variant.
```rust
use parse_display::FromStr;
#[derive(Debug, Eq, PartialEq)]
struct CanNotFromStr;
#[derive(FromStr, Debug, Eq, PartialEq)]
#[allow(dead_code)]
enum HasIgnore {
#[from_str(ignore)]
A(CanNotFromStr),
#[display("{0}")]
B(u32),
}
assert_eq!("1".parse(), Ok(HasIgnore::B(1)));
```
## `#[from_str(default)]`
If this attribute is specified, the default value is used for fields not included in the input.
If an attribute is specified for struct, the struct's default value is used.
```rust
use parse_display::FromStr;
#[derive(FromStr, PartialEq, Debug)]
#[display("{b}")]
#[from_str(default)]
struct MyStruct {
a: u32,
b: u32,
}
impl Default for MyStruct {
fn default() -> Self {
Self { a:99, b:99 }
}
}
assert_eq!("10".parse(), Ok(MyStruct { a:99, b:10 }));
```
If an attribute is specified for field, the field type's default value is used.
```rust
use parse_display::FromStr;
#[derive(FromStr, PartialEq, Debug)]
#[display("{b}")]
struct MyStruct {
#[from_str(default)]
a: u32,
b: u32,
}
impl Default for MyStruct {
fn default() -> Self {
Self { a:99, b:99 }
}
}
assert_eq!("10".parse(), Ok(MyStruct { a:0, b:10 }));
```
## `#[from_str(default_fields(...))]`
You can use `#[from_str(default_fields(...))]` if you want to set default values for the same-named fields of multiple variants.
```rust
use parse_display::FromStr;
#[derive(FromStr, PartialEq, Debug)]
#[display("{}-{a}")]
#[from_str(default_fields("b", "c"))]
enum MyEnum {
VarA { a:u8, b:u8, c:u8 },
VarB { a:u8, b:u8, c:u8 },
}
assert_eq!("VarA-10".parse(), Ok(MyEnum::VarA { a:10, b:0, c:0 }));
assert_eq!("VarB-10".parse(), Ok(MyEnum::VarB { a:10, b:0, c:0 }));
```
## License
This project is dual licensed under Apache-2.0/MIT. See the two LICENSE-\* files for details.
## Contribution
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.