rep

rep is a tiny utility that lets you easily enforce representation/class invariants throughout your Rust data structures.

Representation invariants are logical assertions that must hold true for every mutation of your data structure. For example, in your GIS application, you may have the following rep invariant for a LatLong. rust self.lat >= -90.0 && self.lat <= 90 && self.long >= -180.0 && self.long <= 180

Enforcing representation invariants is easy with rep. Adding invariants to your data structures is just 2 easy steps. 1. Define a correct representation (by implementing CheckRep either manually or with a macro) 2. Insert runtime checks (either manually or with a macro)

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) } ```

We can recursively check representation and use custom functions per field. ```rust fn ishealthvalid(h: u32) -> bool { h > 0 && h < 100 }

[derive(CheckRep)]

struct Player { #[rep(check)] position: Point, #[rep(assertwith = "ishealth_valid")] health: u32 } ```

More advanced rep-checking can be done through custom checking. ```rust fn ishealthvalid(h: u32) -> bool { h > 0 && h < 100 }

[derive(CheckRep)]

struct Player { #[rep(usecustom)] // indicates that custom code should be used #[rep(check)] position: Point, #[rep(assertwith = "ishealthvalid")] health: u32 }

impl CustomCheckRep for Line { fn c_correctness(&self) -> Result<(), Vec> { let mut errors = vec![]; if self.x2 != self.y2 { errors.push(String::from("self.x2 must equal self.y2")); }

    if errors.len() == 0 { Ok(()) } else { Err(errors) }
}

} rust struct Player { position: Point, health: u32 }

impl CheckRep for Player { fn correctness(&self) -> Result<(), Vec> { let mut errors = vec![]; // your code here... if errors.len() == 0 { Ok(()) } else { Err(errors) } } } ```

Once CheckRep is implemented, you may use it with the #[check_rep, #[require_rep, and #[check_rep macros. ``rust // this addscheck_rep` at start and end of all public mutating methods

[check_rep]

impl Device { pub fn turnon(&mut self) {} // requirerep, ensurerep, checkrep add to start, end, start and end respectively #[requirerep] pub fn getvoltage(&mut self, p: Position) {} #[ensurerep] pub fn actuate(&mut self, p: Position, v: Voltage) {} #[checkrep] fn do_something(&self) {} } ```

If a logger is present invariant violation will be logged instead of panicked.

usage

Just add the following to your Cargo.toml file. toml [dependencies] rep = "0.3.0"

Then, in your module. rust use rep::*;