The string:find method in Lua can return multiple values: the start of the match and the end. I can then use unpacking to assign the start and the end to separate variables.
> text = 'ciao pollo mario'
> a, b = text:find('pollo') -- without parentheses
> a, b
6 10
But for some reason, putting parentheses around the find call messes up the unpacking:
> a, b = ( text:find('pollo') ) -- with parentheses
> a, b
6 nil
This is very sad since I use parentheses for code readability, like this:
> a, b = (
text:find('pollo')
)
Why is this happening? I would expect that parentheses don't have any effect on the result!
Because Lua's syntax defines that expressions in parentheses can only be a single expression:
exp ::= nil | false | true | Numeral | LiteralString | ‘...’ | functiondef | prefixexp | tableconstructor | exp binop exp | unop exp
prefixexp ::= var | functioncall | ‘(’ exp ‘)’
This is also mentioned in the manual:
Lua 5.1-5.3 Any expression enclosed in parentheses always results in only one value.
Lua 5.4 As a particular case, the syntax expects a single expression inside a parenthesized expression; therefore, adding parentheses around a multires expression forces it to produce exactly one result.