rust-lang/rust-clippy

Detect creation of new collection when it could be emptied

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#16,520 创建于 2026年2月5日

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 (5 评论) (0 反应) (1 负责人)Rust (10,406 star) (1,391 fork)batch import
A-lintgood first issue

描述

Description

See https://github.com/uutils/coreutils/pull/10695

When a variable holding a collection (such as Vec/VecDeque/HashMap/BTreeMap) is replaced by a new empty instance, it can be more efficient to instead clear the existing one to be able to reuse the allocated memory.

For example, x = Vec::new() can be replaced by x.clear(): x will be an empty vector, except that the storage (and capacity) will be inherited from the previous instance.

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贡献者指南

技术栈
rust
领域
performancetooling
议题类型
feature
难度面向新贡献者的预计实现难度，1 表示很小改动，5 表示专家级工作。
3
预计时间有经验贡献者完成调查、实现、测试并准备 pull request 的粗略时间范围。
1-3 hours
活动状态议题当前的可参与程度：新鲜、活跃、陈旧、阻塞或等待维护者输入。
blocked
清晰度议题是否清楚说明期望改动、验收标准和下一步。
clear
前置要求
RustClippy development setup
新手友好度1-100 的估计分数，表示该议题对首次贡献者的友好程度。
40
研究方向
Review the referenced PR #10695 to understand the pattern where a collection is replaced by a new empty instance. Examine existing Clippy lints that suggest using `.clear()` for similar optimizations to understand the lint structure. The implementation involves creating a new lint that matches assignment expressions like `x = Vec::new()` and suggests replacing with `x.clear()`. Ensure the lint includes proper tests and documentation.