Question

我正在尝试将给定结构的Vec转换为其String并最终转换为&str格式。

此示例代码完全模拟了我要实现的目标。

fn main() {
    let a = vec![1i32, 2i32, 3i32];

    let step1: Vec<String> = a.iter().map(|x| x.to_string()).collect::<Vec<String>>();

    let step2: Vec<&str> = step1.iter().map(AsRef::as_ref).collect::<Vec<&str>>();

    // This does not work as I was expecting it to
    // and its not being accepted by the compiler as valid code
    //
    let in_single_step: Vec<&str> = a
        .iter()
        .map(|x| x.to_string()) // <--- Something is needed after this step?
        .map(AsRef::as_ref)
        .collect::<Vec<&str>>();

    println!("{:?}", in_single_step);
}

playground with this code

我得到一个错误：

error[E0631]: type mismatch in function arguments
  --> src/main.rs:14:10
   |
14 |         .map(AsRef::as_ref)
   |          ^^^
   |          |
   |          expected signature of `fn(std::string::String) -> _`
   |          found signature of `for<'r> fn(&'r _) -> _`

error[E0599]: no method named `collect` found for type `std::iter::Map<std::iter::Map<std::slice::Iter<'_, i32>, [closure@src/main.rs:13:14: 13:31]>, for<'r> fn(&'r _) -> &'r _ {<_ as std::convert::AsRef<_>>::as_ref}>` in the current scope
  --> src/main.rs:15:10
   |
15 |         .collect::<Vec<&str>>();
   |          ^^^^^^^
   |
   = note: the method `collect` exists but the following trait bounds were not satisfied:
           `&mut std::iter::Map<std::iter::Map<std::slice::Iter<'_, i32>, [closure@src/main.rs:13:14: 13:31]>, for<'r> fn(&'r _) -> &'r _ {<_ as std::convert::AsRef<_>>::as_ref}> : std::iter::Iterator`
           `std::iter::Map<std::iter::Map<std::slice::Iter<'_, i32>, [closure@src/main.rs:13:14: 13:31]>, for<'r> fn(&'r _) -> &'r _ {<_ as std::convert::AsRef<_>>::as_ref}> : std::iter::Iterator`

类似的问题是：

如何在一个步骤中将Vec <MyStruct>转换为Vec <String>然后转换为Vec <＆str>？

0 个答案: