[英]Generic supertrait / requiring blanket impl
Currently, I have a trait like this:目前,我有这样的特质:
trait Trait
where
Self: Sized,
{
fn try_form_u8(num: u8) -> Option<Self>;
fn try_from_str<T: AsRef<str>>(s: &T) -> Option<Self>;
// ...
}
Optimally, I want to define it like simliar to this, in order to not have try_from_*
methods outside of a TryFrom
implementation:最佳情况下,我想像这样定义它,以便在
TryFrom
实现之外没有try_from_*
方法:
trait Trait: for<T: AsRef<str>> TryFrom<u8> + TryFrom<T>
where
Self: Sized
{
// ...
}
I couldn't find a way to accomplish that and finally came across this thread: Can a trait have a supertrait that is parameterized by a generic?我找不到实现这一目标的方法,最后遇到了这个线程: 特征可以有一个由泛型参数化的超特征吗?
I wonder how to continue from here.我想知道如何从这里继续。 Should I use the unconventional
try_from_str
method or is there a better way to express what is needed here?我应该使用非常规的
try_from_str
方法还是有更好的方法来表达这里需要的内容?
Note that in my original code I have Path
instead of str
, which could eliminate some special solutions, but I would still like to know them if there are any nice solution!请注意,在我的原始代码中,我使用
Path
而不是str
,这可以消除一些特殊的解决方案,但如果有任何好的解决方案,我仍然想知道它们!
If a type implements TryFrom<&str>
, it is trivial to create it from a String
or Rc<str>
or anything else that is AsRef<str>
.如果一个类型实现了
TryFrom<&str>
,那么从String
或Rc<str>
或任何其他AsRef<str>
创建它是微不足道的。 So let's start with that:让我们从这个开始:
trait Trait: TryFrom<u8> + for<'a> TryFrom<&'a str> {}
It's easy to use this with other types simply by calling .as_ref()
, but if you still want the generic version, you can provide a default implementation:只需调用
.as_ref()
即可轻松将其与其他类型一起使用,但如果您仍然需要通用版本,则可以提供默认实现:
trait Trait: TryFrom<u8> + for<'a> TryFrom<&'a str> {
fn try_from_str<S: AsRef<str>>(arg: &S) -> Result<Self, <Self as TryFrom<&str>>::Error> {
arg.as_ref().try_into()
}
}
This way, implementors of Trait
don't have to write anything special, but users still have the convenient try_from_str
function.这样,
Trait
实现者不必编写任何特殊的东西,但用户仍然可以使用方便的try_from_str
函数。
Path
version Path
版本trait Trait: TryFrom<u8> + for<'a> TryFrom<&'a Path> {
fn try_from_path<P: AsRef<Path>>(arg: &P) -> Result<Self, <Self as TryFrom<&Path>>::Error> {
arg.as_ref().try_into()
}
}
str
version str
版本For str
specifically, you might want to use the standard library trait FromStr
instead of TryFrom
, which is more specialized to this use case, enables str::parse
and does not require a higher-ranked trait bound:特别是对于
str
,您可能希望使用标准库特征FromStr
而不是TryFrom
,后者更专门用于此用例,启用str::parse
并且不需要更高排名的特征边界:
trait Trait: TryFrom<u8> + FromStr {
fn try_from_str<S: AsRef<str>>(arg: &S) -> Result<Self, <Self as FromStr>::Err> {
arg.as_ref().parse()
}
}
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