Macro capturing generic parameters

playground.rs

#![allow(dead_code)]

macro_rules! as_item { ($i:item) => ($i) }

macro_rules! s {
    ($t:ident) => {
        impl $t {
        }
    };
    ($t:ident<$($x:tt),+>) => {
        as_item!(
            impl <$($x),+> $t <$($x),+> {
            }
        );
    }
}

#[derive(Debug)] struct Thing { i: i32 }
#[derive(Debug)] struct OtherThing<'a, 'b, T> { p1: &'a i32, p2: &'b i32, t: T }

s!(Thing);
s!(OtherThing<'a, 'b, T>);

fn main() {
    let a = Thing { i: 42 };
    let b = OtherThing { p1: &a.i, p2: &42, t: "moo" };
    println!("{:?} {:?}", a, b);
}