Suggestion: stricter operators · Microsoft/TypeScript#7989

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描述

Currently operators like "+" are defined such that they match their semantics in JS. The below are all allowed by the compiler and produce the shown values, even with --strictNullChecks on.

2 + 'a' => "2a"
null + 'a' => "nulla" (!)
2 - null => 2

I propose letting users opt in (maybe via some --strictOperators) to strict operator behavior. Concretely I think this means:

restrict +, and += to just number and string, e.g. for the former only declare

function +(a: number, b: number): number;
function +(a: string, b: string): string;

restrict - and -= to just number

(any should continue to work as normal, of course.)

Relevant spec section: https://github.com/Microsoft/TypeScript/blob/master/doc/spec.md#419-binary-operators

See also "Expression operators" in the strictNullTypes change: https://github.com/Microsoft/TypeScript/pull/7140 and in particular this rationale: https://github.com/Microsoft/TypeScript/pull/7140#issuecomment-186432250

This would fall under of "stricter" TypeScript, https://github.com/Microsoft/TypeScript/issues/274 .

贡献者指南

技术栈: typescript
领域: developer experience
议题类型: feature
难度: 4
预计时间: over 1 week
活动状态: stale
清晰度: clear
前置要求: TypeScript type systemcompiler architecturestrictNullChecks implementation
新手友好度: 15
研究方向: Review the TypeScript specification section on binary operators (https://github.com/Microsoft/TypeScript/blob/master/doc/spec.md#419 binary operators). Examine the existing strictNullChecks implementation in PR #7140 and the related rationale in the comments. Understand the compiler's type checking for operators in the checker.ts file. Propose a design that extends the strict mode to include operator restrictions while maintaining compatibility with 'any' type.