A zero-dependency crate for writing repetitive code easier and faster
Check Syntax for information on 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 had an unintuitive syntax for me, so I decided to make my own tool.
```rust
trait Sqrt {
fn dumb_sqrt(self) -> Result
akin! { let &inttype = [i64, u64]; let &negativecheck = [ { if self < 0 { return Err("Sqrt of negative number") } }, NONE ];
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, &'static str> {
*negative_check
match self {
*branch
_ => Err("Sqrt of num not in [1, 4]")
}
}
}
}
Is expanded to:
rust
trait Sqrt {
fn dumb_sqrt(self) -> Result
impl Sqrt for i64 {
fn dumb_sqrt(self) -> Result
match self {
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.
Check the tests/ folder of the repository for more examples.
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.
Also notice that variables end with ;
```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 both have 3 values.
As you can see, & is used to declare variables and * is used to "dereference" them to the current value.
If a used variable has less values than another, the last one will be used.
rust
akin! {
let &v1 = [c];
let &v2 = [a, b];
println!("*v1*v2");
}
Expands to
rust
println!("ca");
println!("cb");
All code in variables must be enclosed in brackets {...}.
```rust
akin! {
let &var = [-1, 1];
let &code = [
{
println!("true");
},
{
println!("false");
}
];
if *var < 0 {
*code
}
}
Will expand to
rust
if -1 < 0 {
println!("true");
}
if 1 < 0 {
println!("false")
}
```
Check the tests/ folder of the repository for more examples.
NONE is the way you can tell akin to simply skip that value and not write anything.
It is useful for when you want to have elements in a duplication that do not have to be in the others.
```rust
akin! { let &num = [1, 2, 3]; let &code = [ NONE, { .pow(2) } ];
println!("*num^2 = {}", *num~u32*code);
// *num~u32 is necessary to ensure the type is written correctly (it would be "1 u32" otherwise)
} ```
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 because '_' is an identifier
fn _ 1()
To avoid it, use the joint modifier `~`, making the next identifier not to be separated.
rust
let &name = [1];
fn _~*name()... // *name is affected by the modifier
// Will get correctly expanded to
fn _1()
``
Inside string literals"..."` it is not necessary to use the modifier, as Rust does not count them as identifiers.
This is a limitation on proc-macro parsing, so I doubt it'll be fixed soon.
Yes, this crate does not use syn nor quote, as parsing the syntax is pretty simple and both add a lot of overhead.
For this reason, akin should not impact compile times as much as most proc-macros, try using it and see it by yourself!