types - 如何避免无约束类型参数错误

Question

如果不使用不受约束的类型，我想不出一种方法来获得以下功能。

struct Things<T> {
    thing: T
}
trait ThingActions<D> {//will be implemented for 'D's of different types
    fn foo(&self, data: D) {}
    fn bar(&self, data: D) {}
}
impl<T: ThingActions<D>, D> Things<T> {
    fn do_foos(&self, data: D) {//any D with corresponding foo can be used here
        self.thing.foo(data)
    }
}
impl<T: ThingActions<D>, D: Send + Sync> Things<T> {
    fn do_bars_multithreaded(&self, data: D) {
        self.thing.bar(&self.thing, data)//this happens in a different thread
    }
}

我的最终目标是让下面的代码适用于 foo 和 bar 的任何配置，而对它的更改相对较少。

fn main(){
    let number = Things {thing: 5isize};
    number.do_foos(2);
    number.do_foos('a');
}
impl ThingActions<isize> for isize {
    fn foo(&self, data: isize){
        println!("{}", data + self)
    }
}
impl ThingActions<char> for isize {
    fn foo(&self, data: char){
        println!("{}, {}", data, self)
    }
}

也有可能的情况是除了“事物”之外什么都不使用。

Answer 1

你可以尝试绑定(bind)D仅在 fn 上，而不是整个结构:

struct Things<T> {
    thing: T
}
trait ThingActions<D> {//will be implemented for 'D's of different types
    fn foo(&self, data: D) {}
    fn bar(&self, data: D) {}
}
impl<T> Things<T> {
    fn do_foos<D>(&self, data: D)
        where T: ThingActions<D>
    {//any D with corresponding foo can be used here
        self.thing.foo(data)
    }
}
impl<T> Things<T> {
    fn do_bars_multithreaded<D>(&self, data: D)
        where T: ThingActions<D>, D: Send + Sync
    {
        self.thing.bar(data)//this happens in a different thread
    }
}

fn main(){
    let number = Things {thing: 5isize};
    number.do_foos(2);
    number.do_foos('a');
}
impl ThingActions<isize> for isize {
    fn foo(&self, data: isize){
        println!("{}", data + self)
    }
}
impl ThingActions<char> for isize {
    fn foo(&self, data: char){
        println!("{}, {}", data, self)
    }
}