Type named capture groups better

Search Terms

named regexp, named capture groups

Motivation

Currently named capture groups are a bit of a pain in TypeScript:

1. All names are of type string even if the regexp doesn't have that named group.
2. You need to use non-null assertion for .groups even when that is the only possibility.

Suggestion

I propose making RegExp higher order on its named capture groups so that .groups is well typed.

// Would have type: RegExp<{ year: string, month: string }>
const date = /(?<year>[0-9]{4})-(?<month>[0-9]{2})/

const match = someString.match(date)
if (match) {
  // match.groups type would be { year: string, month: string }
  // currently is undefined | { [key: string]: string }
}

// Would have type RegExp<{ year: string, month?: string }>
const optionalMonth = /(?<year>[0-9]{4})(-(?<month>[0-9]{2}))?/

Checklist

My suggestion meets these guidelines:

• [✓] This wouldn't be a breaking change in existing TypeScript/JavaScript code
• [✓] This wouldn't change the runtime behavior of existing JavaScript code
• [✓] This could be implemented without emitting different JS based on the types of the expressions
• [✓] This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
• [✓] This feature would agree with the rest of TypeScript's Design Goals.

Issue では実装ファイルやテストは指定されていません。まず RegExp とマッチグループが現在どのように型付けされているかを確認し、次に提案どおり名前付きグループを推論できるかどうかを判断してください。名前付きおよびオプショナルなキャプチャグループが、出力される JavaScript を変更せずに正確に表現されれば完了です。