swiftlang/swift

[SR-5528] Allow multiple typealiases in a declaration

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#48,100 opened on Jul 22, 2017

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 (3 comments) (0 reactions) (1 assignee)Swift (69,989 stars) (10,719 forks)batch import
compilerfeaturegood first issueparserswift evolution proposal neededtype checkertypealias

Description
Previous ID SR-5528
Radar None
Original Reporter @jckarter
Type Bug
Votes 0
Component/s Compiler
Labels Bug, StarterProposal
Assignee None
Priority Medium

md5: 2a0e34842e00129c1149fdebbc72bce0

Issue Description:

https://twitter.com/charlesismcom/status/888488466970955776

It would be consistent with let/var if you could write a comma-separated list of typealiases in one declaration, e.g.:

typealias Tomayto = Tomahto, Potayto = Potahto

Contributor guide

Tech stack
swift
Domain
developer experience
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Swift programmingCompiler basics
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60
Research direction
Examine how 'let' and 'var' declarations support multiple comma separated bindings in the Swift compiler's parser. Look for the parsing logic in the AST and Sema phases for typealias declarations. Review any comments on the issue for existing discussion. Consider implementing a similar pattern for typealias in the parser (e.g., in 'Parser::parseDeclTypeAlias') and updating the type checker accordingly.