Microsoft/TypeScript

typeof Foo['bar'] has strange precedence

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#19,707 创建于 2017年11月3日

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 (6 评论) (0 反应) (0 负责人)TypeScript (48,455 star) (6,726 fork)batch import
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描述

Type queries combined with indexed access types currently produce a parse tree that is surprising in its behavior.

One would think that typeof Foo['bar'] would be parsed as typeof (Foo['bar']), which would really be something like typeof Foo.bar.

That's not the case. It's actually parsed as (typeof Foo)['bar'].

Conveniently, it seems that semantically (when type-checking) these are identical, but it seems strange for syntactic consumers. Do we believe this is currently working as intended?

贡献者指南

技术栈
typescript
领域
toolingdeveloper experience
议题类型
research
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
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1-3 hours
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stale
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
TypeScript type systemcompiler parser basics
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。
30
研究方向
Investigate the parser implementation in src/compiler/parser.ts to see how typeof and indexed access types are parsed. Review the relevant grammar rules and check if the current behavior is deliberate. If not, propose a fix to change the parse tree. Additionally, check if any existing tests cover this precedence.