Compile-time comparison, parsing, and const equivalents of std methods.

Features

This crate provides:

• Compile-time parsing through the [Parser] type, and [parse_any] macro.

• Functions for comparing many standard library types, with the [const_eq]/[const_eq_for]/[const_cmp]/[const_cmp_for] macros for more conveniently calling them, powered by the [polymorphism] module.

• Const fn equivalents of other standard library functions and methods.

Examples

Parsing an enum

This example demonstrates how you can parse a simple enum from an environment variable, at compile-time.

use konst::eq_str;
use konst::{unwrap_opt_or, unwrap_ctx};

#[derive(Debug, PartialEq)]
enum Direction {
Forward,
Backward,
Left,
Right,
}

impl Direction {
const fn try_parse(input: &str) -> Result<Self, ParseDirectionError> {
// As of Rust 1.51.0, string patterns don't work in const contexts
match () {
_ if eq_str(input, "forward") => Ok(Direction::Forward),
_ if eq_str(input, "backward") => Ok(Direction::Backward),
_ if eq_str(input, "left") => Ok(Direction::Left),
_ if eq_str(input, "right") => Ok(Direction::Right),
_ => Err(ParseDirectionError),
}
}
}

const CHOICE: &str = unwrap_opt_or!(option_env!("chosen-direction"), "forward");

const DIRECTION: Direction = unwrap_ctx!(Direction::try_parse(CHOICE));

fn main() {
match DIRECTION {
Direction::Forward => assert_eq!(CHOICE, "forward"),
Direction::Backward => assert_eq!(CHOICE, "backward"),
Direction::Left => assert_eq!(CHOICE, "left"),
Direction::Right => assert_eq!(CHOICE, "right"),
}
}
# #[derive(Debug, PartialEq)]
# pub struct ParseDirectionError;
#
# use std::fmt::{self, Display};
#
# impl Display for ParseDirectionError {
#   fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
#       f.write_str("Failed to parse a Direction")
#   }
# }
#
# impl ParseDirectionError {
#    const fn panic(&self) -> ! {
#        [/*failed to parse a Direction*/][0]
#    }
# }
#
#

Parsing a struct

This example demonstrates how you can use [Parser] to parse a struct at compile-time.

use konst::{ parsing::{Parser, ParseValueResult}, for_range, parse_any, try_rebind, unwrap_ctx, };

const PARSED: Struct = { // You can also parse strings from environment variables, or from an include_str!(....) let input = "
1000, circle, red, blue, green, blue, ";

unwrap_ctx!(parse_struct(Parser::from_str(input))).0 };

fn main(){ assert_eq!( PARSED, Struct{ amount: 1000, repeating: Shape::Circle, colors: [Color::Red, Color::Blue, Color::Green, Color::Blue], } ); }

#[derive(Debug, Clone, PartialEq, Eq)] pub struct Struct { pub amount: usize, pub repeating: Shape, pub colors: [Color; 4], }

#[derive(Debug, Clone, PartialEq, Eq)] pub enum Shape { Circle, Square, Line, }

#[derive(Debug, Copy, Clone, PartialEq, Eq)] pub enum Color { Red, Blue, Green, }

pub const fn parse_struct(mut parser: Parser<'>) -> ParseValueResult<', Struct> { try_rebind!{(let amount, parser) = parser.trim_start().parse_usize()} try_rebind!{parser = parser.strip_prefix(",")}

try_rebind!{(let repeating, parser) = parse_shape(parser.trim_start())} try_rebind!{parser = parser.strip_prefix(",")}

try_rebind!{(let colors, parser) = parse_colors(parser.trim_start())}

Ok((Struct{amount, repeating, colors}, parser)) }

pub const fn parse_shape(mut parser: Parser<'>) -> ParseValueResult<', Shape> { let shape = parse_any!{parser, strip_prefix; "circle" => Shape::Circle, "square" => Shape::Square, "line" => Shape::Line, _ => return Err(parser.into_other_error()) }; Ok((shape, parser)) }

pub const fn parse_colors(mut parser: Parser<'>) -> ParseValueResult<', [Color; 4]> { let mut colors = [Color::Red; 4];

for_range!{i in 0..4 => try_rebind!{(colors[i], parser) = parse_color(parser.trim_start())} try_rebind!{parser = parser.strip_prefix(",")} }

Ok((colors, parser)) }

pub const fn parse_color(mut parser: Parser<'>) -> ParseValueResult<', Color> { let color = parse_any!{parser, strip_prefix; "red" => Color::Red, "blue" => Color::Blue, "green" => Color::Green, _ => return Err(parser.into_other_error()) }; Ok((color, parser)) }

# Cargo features

These are the features of these crates:

- `"cmp"`(enabled by default):
Enables all comparison functions and macros,
the string equality and ordering comparison functions don't require this feature.

- `"parser"`(enabled by default):
Enables the [`parsing`] module, for parsing from `&str` and `&[u8]`.

- `"constant_time_slice"`(disabled by default):<br>
Improves the performance of slice functions that split slices,
from taking linear time to taking constant time,
this requires using some nightly Rust features.
<br>Note that only functions which mention this feature in their documentation are affected.

- `"const_generics"` (disabled by default):
Changes impls for arrays to use const generics instead of only supporting small arrays.
This feature requires Rust 1.51.0.

# No-std support

`konst` is `#![no_std]`, it can be used anywhere Rust can be used.

# Minimum Supported Rust Version

`konst` requires Rust 1.46.0, because it uses looping an branching in const contexts.

Features that require newer versions of Rust, or the nightly compiler,
need to be explicitly enabled with cargo features.



[`const_eq`]: ./macro.const_eq.html
[`const_eq_for`]: ./macro.const_eq_for.html
[`const_cmp`]: ./macro.const_cmp.html
[`const_cmp_for`]: ./macro.const_cmp_for.html
[`polymorphism`]: ./polymorphism/index.html
[`parsing`]: ./parsing/index.html
[`Parser`]: ./parsing/struct.Parser.html
[`parse_any`]: macro.parse_any.html