我正在尝试在特征中找到构造函数的示例,但没有太多运气。这是Rust中惯用的事吗?
trait A {
fn new() -> A;
}
struct B;
impl A for B {
fn new() -> B {
B
}
}
fn main() {
println!("message")
}
<anon>:7:8: 9:9 error: method `new` has an incompatible type for trait: expected trait A, found struct `B` [E0053]
<anon>:7 fn new() -> B {
<anon>:8 B
<anon>:9 }
<anon>:7:8: 9:9 help: see the detailed explanation for E0053
error: aborting due to previous error
playpen: application terminated with error code 101
转换它会返回一个core :: marker :: Sized相关错误。
trait A {
fn new() -> A;
}
struct B;
impl A for B {
fn new() -> A {
B as A
}
}
fn main() {
println!("message")
}
<anon>:8:10: 8:16 error: cast to unsized type: `B` as `A`
<anon>:8 B as A
^~~~~~
<anon>:8:10: 8:11 help: consider using a box or reference as appropriate
<anon>:8 B as A
^
<anon>:7:20: 7:21 error: the trait `core::marker::Sized` is not implemented for the type `A + 'static` [E0277]
<anon>:7 fn new() -> A {
^
<anon>:7:20: 7:21 note: `A + 'static` does not have a constant size known at compile-time
<anon>:7 fn new() -> A {
^
error: aborting due to 2 previous errors
playpen: application terminated with error code 101
答案 0 :(得分:9)
您需要使用Self
类型。在特征声明中,Self
指的是实现特征的类型。在您的情况下,特征声明应如下所示:
trait A {
fn new() -> Self; // Self stands for any type implementing A
}
您的原始版本略有不同,因为它将返回trait object,而不是实现者类型的值。