我正在使用与embedded_hal
接口(尤其是stm32f4xx-hal
)兼容的硬件抽象层,在Rust中为STM32 cortex-m微控制器开发应用程序。
我想实现一个冗长的读取功能,该功能可打印出通用串行端口上收到的内容,并在出错时显示额外的消息。
我的初稿如下:
fn read<T: embedded_hal::serial::Read<u8>>(port: &mut T) {
match nb::block!(port.read()) {
Ok(byte) => hprintln!("received {}", byte),
Err(hal::serial::Error::Overrun) => hprintln!("Overrun Error"),
Err(_) => hprintln!("Unknown error"),
}.ok();
}
不幸的是,编译器抱怨无法将序列Error
枚举与与Error
特性相关联的Read
类型调和:
error[E0308]: mismatched types
--> src/peripherals/cctalk.rs:95:13
|
93 | match nb::block!(port.read()) {
| ----------------------- this expression has type `core::result::Result<u8, <T as embedded_hal::serial::Read<u8>>::Error>`
94 | Ok(byte) => hprintln!("received {}", byte),
95 | Err(hal::serial::Error::Overrun) => hprintln!("Overrun Error"),
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected associated type, found enum `stm32f4xx_hal::serial::Error`
|
= note: expected associated type `<T as embedded_hal::serial::Read<u8>>::Error`
found enum `stm32f4xx_hal::serial::Error`
help: consider constraining the associated type `<T as embedded_hal::serial::Read<u8>>::Error` to `stm32f4xx_hal::serial::Error`
|
92 | fn read<T: embedded_hal::serial::Read<u8, Error = stm32f4xx_hal::serial::Error>>(port: T) {
|
在这一点上,我认为应该为特征指定一个附加约束:
fn read<T: embedded_hal::serial::Read<u8>>(port: &mut T) {
// Read::Error must be equal to hal::serial::Error
where <T as embedded_hal::serial::Read<u8>>::Error = hal::serial::Error,
{
match nb::block!(port.read()) {
Ok(byte) => hprintln!("received {}", byte),
Err(hal::serial::Error::Overrun) => hprintln!("Overrun Error"),
Err(_) => hprintln!("Unknown error"),
}.ok();
}
这时出现错误,指出在where子句中尚不支持相等约束。
error: equality constraints are not yet supported in `where` clauses
--> src/peripherals/cctalk.rs:94:1
|
94 | <T as embedded_hal::serial::Read<u8>>::Error = hal::serial::Error,
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not supported
|
= note: see issue #20041 <https://github.com/rust-lang/rust/issues/20041> for more information
help: if `Error` is an associated type you're trying to set, use the associated type binding syntax
|
94 | T: embedded_hal::serial::Read<u8, Error = hal::serial::Error>,
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
在这里,我对Rust的有限经验不足。我知道应该以某种方式使embedded_hal::serial::Read<u8>::Error
与hal::serial::Error
相同,但是我不确定(如果可能)如何。我应该如何进行?
答案 0 :(得分:1)
尽管特征Read
的{{1}}没有参数,但可以使用以下语法约束关联的Error
类型:
Error
在撰写本文时, /*Associated types can be referred
to between angular braces like this,
similarly to struct fields.*/
fn read<T: embedded_hal::serial::Read<u8, Error = hal::serial::Error>>(port: &mut T)
// ...
1.45.0中没有办法在相应的rustc
子句中满足此要求。