Rust 类型 + 寿命的总和是多少？

Question

There's a trait that does this:

pub trait Device<'a> {
    type RxToken: RxToken + 'a;
    type TxToken: TxToken + 'a;

What dos this mean? Why not type RxToken: RxToken<'a> ?

Answer 1

Let's see an example:

trait SayHello {
    fn say_hello(&self);
}

pub trait Device<'a> {
    type MyType : SayHello + 'a;
}

As you see, SayHello itself does not know anything about lifetime constraints, but MyType is constrained to satisfy SayHello and must be valid for lifetime 'a .

In contrast, consider

trait SayHello {
    fn say_hello(&self);
}

pub trait Device2<'a> {
    type MyType : SayHello;
}

Here, Device2 has no lifetime requirements for MyType - it only needs to satisfy SayHello .