Rust中Option、Result的map和and_then的区别

晴雷2023-10-10 14:59

rust 复制代码

Maps a Result<T, E> to Result<U, E> by applying a function to a contained Ok value, leaving an Err value untouched.
This function can be used to compose the results of two functions.
#[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),
    }
}
Calls op if the result is Ok, otherwise returns the Err value of self.
This function can be used for control flow based on Result values.
#[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),
    }
}

看签名这两个函数返回值都是Result，不同之处在于闭包的返回值，and_then要求我们手动包起来。

map和and_then最大区别就是map在链式调用时可能会出现嵌套的Option或者Result.

如果闭包函数返回值也是一个Option\Result的话，那么整体结果就会出现嵌套，此时使用and_then就可以避免.