rust - 为什么特质不能 self 构建？

Question

这段代码给我一个编译错误:

trait IBoo {
    fn new() -> Box<IBoo>;
}

虽然这段代码编译没有任何错误:

trait IBoo {
    //fn new() -> Box<IBoo>;
}

trait IFoo {
    fn new() -> Box<IBoo>;
}

1. 为什么第一个不编译？ rustc --explain E0038 没有直接提示我为什么不可能。
2. 是否可以将构造和方法组合在一个接口(interface)(特征)中？

Answer 1

这是来自 description of E0038 :

Method has no receiver

Methods that do not take a self parameter can't be called since there won't be a way to get a pointer to the method table for them.

trait Foo {
    fn foo() -> u8;
}

This could be called as <Foo as Foo>::foo(), which would not be able to pick an implementation.

Adding a Self: Sized bound to these methods will generally make this compile.

trait Foo {
    fn foo() -> u8 where Self: Sized;
}

你可以这样做:

trait IBoo {
    fn new() -> Box<IBoo>
    where
        Self: Sized;
}

在其他情况下，您可以对整个 impl 进行限制: