Grammar missing optional parens for type identifiers in type inheritance clause #299
Description
Location
Description
The grammar does not currently allow for parenthesized type identifiers in type inheritance clauses.
Current grammar:
type-inheritance-clause → : type-inheritance-list
type-inheritance-list → attributes? type-identifier | attributes? type-identifier , type-inheritance-list
Program that isn't derivable with current grammar:
protocol DefaultItem {}
protocol Item: (DefaultItem) {}
This applies to type inheritance clauses in general.
See an example with class inheritance:
class Class {}
class OtherClass: (Class) {}
Correction
Restructure the grammar to allow for parenthesized type identifiers in type inheritance classes.
Possible Solution:
type-inheritance-clause → : type-inheritance-list
type-inheritance-list → attributes? type-identifier | attributes? ( type-identifier ) | attributes? type-identifier , type-inheritance-list | attributes? ( type-identifier ), type-inheritance-list
This is just one solution but there are other, possibly cleaner, options.
Can also consider changing the productions for type to allow:
type -> type-identifier
along with
type -> (type-identifier)
This is cleaner but would allow any type-identifier to be parenthesized which may cause unintended side effects in other areas of the language.