标准库的Result源码学习。
1. 基础结构
#[must_use = "this `Result` may be an `Err` variant, which should be handled"]
pub enum Result<T, E> {
/// Contains the success value
#[lang = "Ok"]
#[stable(feature = "rust1", since = "1.0.0")]
Ok(#[stable(feature = "rust1", since = "1.0.0")] T),
/// Contains the error value
#[lang = "Err"]
#[stable(feature = "rust1", since = "1.0.0")]
Err(#[stable(feature = "rust1", since = "1.0.0")] E),
}
学习点
#[must_use]属性确保开发者必须处理可能的错误- 使用泛型
T和E支持任何类型 #[lang]属性表示这是语言项(lang item)
2. 基础方法：is_ok和is_err
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub const fn is_ok(&self) -> bool {
matches!(*self, Ok(_))
}
学习点
#[inline]提示编译器内联优化const fn表示编译期可求值- 使用
matches!宏进行模式匹配
3. 所有权管理：as_ref
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub const fn as_ref(&self) -> Result<&T, &E> {
match *self {
Ok(ref x) => Ok(x),
Err(ref x) => Err(x),
}
}
学习点
- 返回引用避免所有权转移
- 使用
ref模式匹配获取引用 - 保持原始
Result不变
4. 组合子：map
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn map<U, F: FnOnce(T) -> U>(self, op: F) -> Result<U, E> {
match self {
Ok(t) => Ok(op(t)),
Err(e) => Err(e),
}
}
学习点
- 高阶函数的使用
FnOncetrait bound允许消费值的闭包- 模式匹配解构
self
5. 链式调用：and_then
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn and_then<U, F: FnOnce(T) -> Result<U, E>>(self, op: F) -> Result<U, E> {
match self {
Ok(t) => op(t),
Err(e) => Err(e),
}
}
学习点
- 错误传播模式
- 闭包作为参数
- 组合操作的优雅方式
6. ?操作符
#[unstable(feature = "try_trait_v2", issue = "84277")]
#[rustc_const_unstable(feature = "const_convert", issue = "88674")]
impl<T, E> ops::Try for Result<T, E> {
type Output = T;
type Residual = Result<!, E>;
#[inline]
fn from_output(output: Self::Output) -> Self {
Ok(output)
}
#[inline]
fn branch(self) -> ControlFlow<Self::Residual, Self::Output> {
match self {
Ok(v) => ControlFlow::Continue(v),
Err(e) => ControlFlow::Break(Err(e)),
}
}
}
学习点
- 操作符重载
- 控制流抽象
- 编译器魔法背后的实现
7. 迭代器集成
#[stable(feature = "rust1", since = "1.0.0")]
impl<T, E> IntoIterator for Result<T, E> {
type Item = T;
type IntoIter = IntoIter<T>;
#[inline]
fn into_iter(self) -> IntoIter<T> {
IntoIter { inner: self.ok() }
}
}
学习点
- 迭代器模式
- 类型转换
- 零成本抽象