3 releases
0.1.2 | Jan 21, 2019 |
---|---|
0.1.1 | Jan 5, 2019 |
0.1.0 | Jan 3, 2019 |
#20 in #from-str
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33KB
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adhoc_derive
Experimental: Derive FromStr impl based on regex provided via attribute
Usage
Add the following in your Cargo.toml:
[dependencies]
adhoc_derive = "0.1.2"
lazy_static = "1.2.0"
regex = "1.1.0"
Then, you can derive a std::str::FromStr
impl as follows:
use adhoc_derive::FromStr;
#[derive(FromStr)]
#[adhoc(regex = r"^#(?P<id>\d+) @ (?P<x>\d+),(?P<y>\d+): (?P<width>\d+)x(?P<height>\d+)$")]
struct Rectangle {
id: usize,
x: usize,
y: usize,
width: usize,
height: usize,
}
let rect: Rectangle = "#123 @ 3,2: 5x4".parse().unwrap();
assert_eq!(123, rect.id);
assert_eq!(3, rect.x);
assert_eq!(2, rect.y);
assert_eq!(5, rect.width);
assert_eq!(4, rect.height);
In general, each field of the struct needs to implement std::str::FromStr
and each field identifier needs to correspond to a named capture group in the regex.
For enums, you need to annotate each variant with a regex. The first regex that matches (usually the only one) determines which variant is instantiated:
#[derive(Debug, PartialEq, FromStr)]
enum Expression {
#[adhoc(regex = r"^$")]
Empty,
#[adhoc(regex = r"^(?P<0>\d+)$")]
Number(i32),
#[adhoc(regex = r"^(?P<a>\d+)\+(?P<b>\d+)$")]
Sum(#[adhoc(construct_with = "a: i32 + b: i32")] i32),
#[adhoc(regex = r"^(?P<a>\d+)-(?P<b>\d+)$")]
Difference(#[adhoc(construct_with = "a: i32 - b: i32")] i32),
}
let empty: Expression = "".parse().unwrap();
assert_eq!(Expression::Empty, empty);
let number: Expression = "4".parse().unwrap();
assert_eq!(Expression::Number(4), number);
let sum: Expression = "8+15".parse().unwrap();
assert_eq!(Expression::Sum(23), sum);
let difference: Expression = "16-23".parse().unwrap();
assert_eq!(Expression::Difference(-7), difference);
For a more comprehensive guide, refer to GUIDE.md
Limitations
This crate is experimental and has a lot of rough edges. In no particular order:
- Doesn't work with generic structs out of the box (it should work if you add the required trait bounds yourself)
- Not yet implemented: optional patterns, i.e. (...)? =>
Option<...>
- Not yet implemented: repeating patterns, i.e. (...)* =>
Vec<...>
- Error handling and especially reporting is basically non-existent
- Provided regex is not validated at compile-time
Dependencies
~5MB
~99K SLoC