Too small to be a RFC and too complicated to be a PR. I guess this is the best place but if not, feel free to suggest another location.
Proposal
macro_metavar_expr is an approved feature that unfortunately created divergent opinions after its acceptance, which ended up blocking stabilization.
In hopes of making some progress, two approaches based on the feedback provided so far will be proposed here.
1. Innermost vs Outermost indexes
count uses outermost indices while length uses innermost indices and this inconsistency creates unnecessary confusion.
To improve the situation, the order of all elements should start from the innermost index to the outermost index.
Mentions
2. $ prefix
Taking count as an example, should the syntax be count(some_metavariable) or count($some_metavariable)? The original RFC specified that metavariable expressions should refer metavariables without $ prefixes but there were some arguments in favour of $.
For unblocking purposes, the requirement of $ is being proposed. Such enforcement doesn't appear to incur a significant overhead besides the additional typing and interactions with $$ or multiple $$s shouldn't be a problem as long as the final expanded $ refers a metavariable.
Mentions
Mentors or Reviewers
@c410-f3r
Process
The main points of the [Major Change Process][MCP] are as follows:
Too small to be a RFC and too complicated to be a PR. I guess this is the best place but if not, feel free to suggest another location.
Proposal
macro_metavar_expris an approved feature that unfortunately created divergent opinions after its acceptance, which ended up blocking stabilization.In hopes of making some progress, two approaches based on the feedback provided so far will be proposed here.
1. Innermost vs Outermost indexes
countuses outermost indices whilelengthuses innermost indices and this inconsistency creates unnecessary confusion.To improve the situation, the order of all elements should start from the innermost index to the outermost index.
Mentions
2.
$prefixTaking
countas an example, should the syntax becount(some_metavariable)orcount($some_metavariable)? The original RFC specified that metavariable expressions should refer metavariables without$prefixes but there were some arguments in favour of$.For unblocking purposes, the requirement of
$is being proposed. Such enforcement doesn't appear to incur a significant overhead besides the additional typing and interactions with$$or multiple$$s shouldn't be a problem as long as the final expanded$refers a metavariable.Mentions
$$in Rust 1.63.0 rust#95860 (comment)$$in Rust 1.63.0 rust#95860 (comment)$$in Rust 1.63.0 rust#95860 (comment)$$in Rust 1.63.0 rust#95860 (comment)Mentors or Reviewers
@c410-f3r
Process
The main points of the [Major Change Process][MCP] are as follows:
@rustbot second.-C flag, then full team check-off is required.@rfcbot fcp mergeon either the MCP or the PR.