调用非泛型特征方法时的泛型类型参数

Question

我有一个特征Command<P>，它有两个类似的函数：

trait Client<P> {}
trait Command<P> {
fn help(&self) -> String;
fn exec(&self, client: &dyn Client<P>) -> String;
}
struct ListCommand {}
impl<P> Command<P> for ListCommand {
fn help(&self) -> String {
return "This is helptext".to_string();
}
fn exec(&self, client: &dyn Client<P>) -> String {
self.help()
}
}
fn main() {
println!("Hello!");
}

Rust抱怨我无法在exec()中调用self.help()，并出现以下错误：

error[E0282]: type annotations needed
--> srcmain.rs:15:14
|
15 |         self.help()
|              ^^^^ cannot infer type for type parameter `P` declared on the trait `Command`

^游乐场

如何指定Self上调用方法的类型注释？

Answer 1

我可以想出三种方法：

• Command::<P>::help(self)
• <Self as Command<P>>::help(self)(或ListCommand而非Self(
• (self as &dyn Command<P>).help()(我想知道是否有不涉及dyn的变体。(