rep

Rep is a small tool for checking representation/class invariants. As programmers, we should care about correctness at compile time and at run time. We should care about our data structures being correct. Rep is a small tool that lets you do 2 things. 1. Define a correct representation (a rep/class invariant) 2. Insert runtime checks (rep checks)

some examples

We can start off with a simple data structure. ```rust use rep::*;

pub struct Line { x1: i32, y1: i32, x2: i32, y2: i32 } The `CheckRep` trait can be implemented. This serves as a definition of correct representation. rust impl CheckRep for Line { fn is_correct(&self) -> bool { self.x1 != self.x2 && self.y1 != self.y2 } } Now we can use the `#[check_rep]` macro to automatically insert calls to `check_rep` at start and end of all methods that are `pub` and mutate `&mut self`. We can also manually make calls to `check_rep` wherever we so desire. rust

[checkrep] // <-- this inserts calls to checkrep at start and end of move_by

impl Line { pub fn new() -> Self { let new_line = Self { x1: -1, y1: -1, x1: 1, y1: 1 };

    new_line.check_rep();
    new_line
}

pub fn move_by(&mut self, x: i32, y: i32) {
    self.x1 += x;
    self.x2 += x;
    self.y1 += y;
    self.y2 += y;
}

} ```

some more examples

For simple representations, we can even derive an implementation of CheckRep. ```rust

[derive(CheckRep)]

struct Circle { x: i32, y: i32, #[rep(assertgt = 0)] #[rep(assertle = 2048)] r: i32, } rust struct Parser { #[rep(assertdefault)] uncloseddelims: (usize, usize, usize) // this is representing (parens, braces, brackets) } ```

usage

Just add the following to your Cargo.toml file. toml [dependencies] rep = "0.2.0"

Then you can begin defining representations and improving the safety of your software.