Crate for writing repetitive code easier and faster. Check Syntax for information about how to use it.
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.
```rust
trait Sqrt {
fn dumb_sqrt(self) -> Result
akin! { let &inttype = [i64, u64]; let &negativecheck = [ 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:
```rust
trait Sqrt {
fn dumbsquareroot(self) -> Result
impl Sqrt for i64 {
fn dumb_sqrt(self) -> Result
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
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.
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.
```rust 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.
rust
let &lhs = [1, 2, 3];
let &rhs = [4, 5, 6];
println!("*lhs + *rhs = {}", *lhs + *rhs);
Will get expanded to:
rust
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.
Now let's describe what the main example is doing. Firstly, we declare the variables that will differentiate each copy of the function.
So, as we need an implementation for i64 and u64, we use them for this purpose.
rust
let &int_type = [i64, u64];
```rust
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 *inttype {
fn dumbsqrt(self) -> Result
match self {
*branch
_ => Err("Sqrt of num not in [1, 4]")
}
}
} ```
By default, akin places a space between all identifiers
rust
let name = 5; // 'name' is an identifier
^^^^
Sometimes, this is not desirable, for example, if trying to interpolate between a function name
```rust
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.
rust
let &name = [1];
fn #*name()... // *name() is affected by the modifier
// Will get correctly expanded to
fn _1()
```
This is a limitation on procmacro parsing, so I doubt it'll be fixed soon.