duang

Rust doesn't support default function arguments and named function arguments.

This crate generate an macro interface for a given function that can be invoked with named arguments and fill the default argument, meanwhile keep the old function intact.

Generating macro interface

In order to generate macro for a function, we just need to wrap the definition with duang!{...}.

```rust use duang::duang;

duang!( pub fn foo(a: T,b: f64 = 13.0, c: T = a*a) -> (T,f64,T) where T: std::ops::Mul, T: std::fmt::Display, T: Copy, { (a,b,c) } ); ```

Invoke

rust use demo_duang::foo; // pass assert_eq!(foo!(1, c = 30, b = -2.0), (1, -2.0, 30)); // pass assert_eq!(foo!(a = 10), (10, 13.0, 100)); // fail // foo!(1,c=30,c=2);

Features

• Support generics, existensial type.
• Friendly error message.

Common issues

Use local variable in default value.

In order to use the generated macro in other crate, users should add $crate and path of the variable used. Also, the variable should be visible(pub) for the scope where the macro is invoked.

rust mod bar { use duang::duang; pub static NUM: i32 = 42; duang!( pub fn foo(a: i32 = $crate::bar::NUM) -> i32 { a } ); } fn main() { use bar::foo; assert_eq!(foo!(), 42); }

Limitations

• Don't support associated function.
• Wildchar can not be used in pattern argument. For example fn foo((a,_): (i32, i32)) is illegal.

TODO

• Generate document for function or macro.
• After "Attributes in formal function parameter position"(#60406) stabilize, change function-like macros to attribute-like macros.

License: MIT