如何添加泛型约束

我无法找出如何限制泛型类型。看起来像K需要实施core::cmp::Eq and core::hash::Hash特征。我无法在文档中找到所需的语法。

use std::collections::HashMap;

struct Foo<K, V> {
    map: HashMap<K, V>,
}

impl<K, V> Foo<K, V> {
    fn insert_something(&mut self, k: K, v: V) {
        self.map.insert(k, v);
    }
}

编译器错误是：

error[E0599]: no method named `insert` found for struct `std::collections::HashMap<K, V>` in the current scope
 --> src/lib.rs:9:18
  |
9 |         self.map.insert(k, v);
  |                  ^^^^^^ method not found in `std::collections::HashMap<K, V>`
  |
  = note: the method `insert` exists but the following trait bounds were not satisfied:
          `K: std::cmp::Eq`
          `K: std::hash::Hash`
// Edit note, the question is old so the error message from the compiler already hint about the answer, but ignore that.

在哪里可以添加约束K?

首先你可以导入 Hash 特征，use std::hash::Hash;.

您可以在 impl 上添加约束：

impl<K: Eq + Hash, V> Foo<K, V>

或者，使用新的“where”语法

impl<K, V> Foo<K, V>
where
    K: Eq + Hash,

您可以参考书中关于特质界限的章节有关约束的更多背景信息。