Rust for Java Programmers | Rust 面向 Java 程序员

Generic Constraints
泛型约束

What you’ll learn: How trait bounds and where clauses compare to Java generic bounds.
本章将学习： trait bound 和 where 子句分别怎样对应 Java 的泛型约束。

Difficulty: 🟡 Intermediate
难度： 🟡 中级

Java developers know bounds such as <T extends Comparable<T>>. Rust expresses similar ideas through trait bounds.
Java 开发者很熟悉 <T extends Comparable<T>> 这种写法。Rust 则通过 trait bound 表达类似意思。

#![allow(unused)]
fn main() {
fn sort_and_print<T: Ord + std::fmt::Debug>(items: &mut [T]) {
    items.sort();
    println!("{items:?}");
}
}

The same bounds can be moved into a where clause for readability:
如果约束太长，也可以挪进 where 子句提升可读性：

#![allow(unused)]
fn main() {
fn sort_and_print<T>(items: &mut [T])
where
    T: Ord + std::fmt::Debug,
{
    items.sort();
    println!("{items:?}");
}
}

Key Difference from Java
和 Java 的关键差异

Rust bounds are closely tied to behavior required by the compiler and standard library traits. They are not just nominal inheritance constraints.
Rust 里的约束更紧密地绑定在行为能力上，通常是编译器和标准库 trait 真正需要的能力，而不只是名义上的继承关系。

Advice
建议

• use inline bounds for short signatures
  签名短时直接写内联约束。
• use where clauses when bounds become long
  约束一长，就改用 where。
• think in capabilities, not class hierarchies
  思考方式优先放在“能力”，不是类层级。