Rust 如何使用trait方法的默认实现而不是类型'；什么是自定义实现？

有些trait方法有默认实现，可以被实现者覆盖。如何为覆盖默认值的结构使用默认实现

例如：

trait SomeTrait {
    fn get_num(&self) -> i32;
    fn add_to_num(&self) -> i32 {
        self.get_num() + 1
    }
}

struct SomeStruct;
impl SomeTrait for SomeStruct {
    fn get_num(&self) -> i32 {
        3
    }
    fn add_to_num(&self) -> i32 {
        self.get_num() + 2
    }
}

fn main() {
    let the_struct = SomeStruct;
    println!("{}", the_struct.add_to_num()); // how can I get this to print 4 instead of 5?
}

---

我提出的一个解决方案是定义一个虚拟结构，其中包含我想要更改的结构。然后，我可以选择哪些方法要覆盖，哪些方法要保留为默认方法

要扩展原始示例，请执行以下操作：

trait SomeTrait {
    fn get_num(&self) -> i32;
    fn add_to_num(&self) -> i32 {
        self.get_num() + 1
    }
}

struct SomeStruct;

impl SomeTrait for SomeStruct {
    fn get_num(&self) -> i32 {
        3
    }
    fn add_to_num(&self) -> i32 {
        self.get_num() + 2
    }
}

fn main() {
    struct SomeOtherStruct {
        base: SomeStruct,
    }

    impl SomeTrait for SomeOtherStruct {
        fn get_num(&self) -> i32 {
            self.base.get_num()
        }
        //This dummy struct keeps the default behavior of add_to_num()
    }

    let the_struct = SomeStruct;
    println!("{}", the_struct.add_to_num());

    //now we can call the default method using the original struct's data.
    println!("{}", SomeOtherStruct { base: the_struct }.add_to_num());
}

---

如果

impl-Deref for SomeOtherStruct

where

Deref

，则可以调用“超类”方法，如

some\u other\u struct.Deref（）.add\u to\u num（）