The expression { a: 1 } is not a problem,

but Rubocop's point( Lint/Syntax: unexpected token tCOLON(Using Ruby 3.1 parser; configure using TargetRubyVersion parameter, under AllCops) ) appears in the expression puts { a: 1 }.

Does anyone know why this statement is against the rules? If you have a reference, I would appreciate it if you could also give me the URL of it.

I use rubocop version 1.24.1 and set TargetRubyVersion in .rubocop.yml. ruby versions 2.7, 3.0 and 3.1 were all tested with the same result.

CodePudding user response：

Braces in Ruby are used for two things: blocks and hashes. And the Ruby parser isn't going to perform infinite lookahead to determine which one it's looking at. If the current syntactic context accepts a block, Ruby assumes the thing you've given it with braces is a block.

puts { a: 1 }

First, we parse puts. It's an identifier, and it's not a local variable, so we'll assume it's a method on the current (main) object. Now we see {. It could be either a hash or a block. And we just parsed an identifier starting a function call, so a block would make sense here. Let's parse it as a block.

Next we see a. Okay, that's fine. A block with no arguments, and we've got an identifier called a. Again, it's not a local variable, so it must be a method on main. Then we see : and that doesn't work. There's no way a : can appear at this point in the syntax, so it's an error. Ruby does not go back and try the "hash" option; it's already committed completely to parsing a block, and that failed.

To call puts with a single hash argument, use parentheses to disambiguate.

puts({ a: 1 })