我正在尝试在为特征实现生成签名的宏中索引数据元组，但有一些错误。我可以索引元组还是需要其他解决方案？破解tuple_index我在谷歌找到的，但它对我不起作用。
macro_rules! expr { ($x:expr) => ($x) } // HACK
macro_rules! tuple_index {
($tuple:expr, $idx:tt) => { expr!($tuple.$idx) }
}
macro_rules! gen_packer {
(@step $data: expr, $_idx:expr,) => {};
(@step $data: expr, $idx:expr, $T:ident, $($tail:ident,)*) => {
// out.append(&mut $T::pack(tuple_index!(data,$idx)));
tuple_index!($data, $idx);
gen_packer!(@step $data, $idx + 1, $($tail,)*);
};
($($T:ident),*) => {
impl<$($T,)+> Packer<($($T,)+)> for Iproto
where $($T: Pack<$T>,)+
{
fn pack(self, data: ($($T,)+)) -> Vec<u8> {
let mut out = vec![];
gen_packer!(@step data, 0, $($T,)*);
return out
}
}
}
}
gen_packer!(A);
编译错误：
error: unexpected token: `0`
--> src/lib/iproto.rs:70:29
|
70 | tuple_index!($data, $idx);
| ^^^^
...
99 | gen_packer!(A);
| --------------- in this macro invocation
error: unexpected token: `,`
--> src/lib/iproto.rs:63:46
|
63 | ($tuple:expr, $idx:tt) => { expr!($tuple.$idx) }
| ^
...
99 | gen_packer!(A);
| --------------- in this macro invocation
error: no rules expected the token `0`
--> src/lib/iproto.rs:70:29
|
61 | macro_rules! expr { ($x:expr) => ($x) } // HACK
| ----------------- when calling this macro
...
70 | tuple_index!($data, $idx);
| ^^^^ no rules expected this token in macro call
...
99 | gen_packer!(A);
| --------------- in this macro invocation
error: aborting due to 3 previous errors