akin

Crate for writing repetitive code easier and faster. Check Syntax for information about how to use it.

Why?

I've found myself having to write a lot of repetitive code (mostly when matching against enums in parsing).
The fantastic duplicate lacked the ability to write invariable code (that didn't get duplicated) and had a too different syntax, so I decided to make my own tool.

Example

trait Sqrt {
    fn dumb_sqrt(self) -> Result<f64, &str>;
}

akin! {
    let &int_type = [i64, u64];
    let &negative_check = [
        if num < 0 {
            return Err("Sqrt of negative number")
        }, 
        //
    ]
    
    let &num = [1,    2,    3, 4];
    let &res = [1, 1.41, 1.73, 2];
    let &branch = {
        *num => Ok(*res),
    }

    impl Sqrt for *int_type {
        fn dumb_sqrt(self) -> Result<f64, &str> {
            *negative_check
            
            match self {
                *branch
                _ => Err("Sqrt of num not in [1, 4]")
            }
        }
    }
}

Is expanded to:

trait Sqrt {
    fn dumb_square_root(self) -> Result<f64, &str>;
}

impl Sqrt for i64 {
    fn dumb_sqrt(self) -> Result<f64, &str> {
        if num < 0 {
            return Err("Sqrt of negative number")
        }

        match num {
            1 => Ok(1),
            2 => Ok(1.41),
            3 => Ok(1.73),
            4 => Ok(2),
            _ => Err("Sqrt of num not in [1, 4]")
        }
    }
}

impl Sqrt for u64 {
    fn dumb_sqrt(self) -> Result<f64, &str> {
        match num {
            1 => Ok(1),
            2 => Ok(1.41),
            3 => Ok(1.73),
            4 => Ok(2),
            _ => Err("Sqrt of num not in [1, 4]")
        }
    }
}

The good thing about akin is that it detects automatically the number of values of each variable for each scope, so for example "branch" will get copied 4 times (as "num" and "res" both have 4 values), but the main function will only be duplicated once, as all the variables it has have 2 values.

Syntax

The crate only provides one macro, akin!. The syntax is as follows:

First, you declare the variables you'll use. A variable name must start with &, as it's the only way it can differentiate between macro or real declarations.

let &variable = [v1, v2, v3, ...]
let &variable2 = [...]
    
let &code = {
    ...
}

Then, when all variables have been declared, you can write the code snippet you want to duplicate.
The amount of times it will be duplicated depends on the variables that are used.

let &lhs = [1, 2, 3];
let &rhs = [4, 5, 6];
println!("*lhs + *rhs = {}", *lhs + *rhs);

Will get expanded to:

println!("1 + 4 = {}", 1 + 4);
println!("2 + 5 = {}", 2 + 5);
println!("3 + 6 = {}", 3 + 6);

Because the variables &lhs and &rhs have 3 values.

As you can see, & is used to declare variables and * is used to "dereference" them to the current value.

Raw modifier

By default, akin places a space between all identifiers

let name = 5; // 'name' is an identifier
        ^^^^

Sometimes, this is not desirable, for example, if trying to interpolate between a function name

    let &name = [1];
    fn _*name()...
    
    // Will get wrongly expanded to, because '_' is an identifier
    fn _ 1()

To avoid it, use the raw # modifier, making the identifier next to the one it affects to not be separated.

let &name = [1];
fn #_*name()... // *name() is affected by the modifier
// Will get correctly expanded to
fn _1()

This is a limitation on proc_macro parsing, so I doubt it'll be fixed soon.