Could you help me understand why the following code works:
def activity_params
params.require(:activity).permit(:name, :description, :location, :user_id, category_ids: [])
end
Yet when I put the array somewhere in the middle instead of last, I get a syntax error:
def activity_params
params.require(:activity).permit(:name, :description, :location, category_ids: [], :user_id)
end
Ruby lets you skip a lot of punctuation that other languages require. In this case, Ruby is making some assumptions about your syntax that may not be obvious. Here's how it's being parsed:
permit(:name, :description, :location, :user_id, { :category_ids => [] })
permit is receiving 5 arguments: 4 symbols, and one hash. In arguments to methods, the last parameter can be a hash but without the hash literal notation of {}.
When you move that hash syntax to the middle of the argument list, it's no longer last, and therefore considered a syntax error.
Knowing this, I believe that if you make it an explicit hash, then it should work here:
permit(:name, :description, :location, { category_ids: [] }, :user_id)
Keyword arguments (named arguments that end in a colon) must come after all positional arguments, as described in the Arguments documentation:
When mixing keyword arguments and positional arguments, all positional arguments must appear before any keyword arguments.
Your category_ids is a keyword argument and the others are symbols treated as positional arguments, which is why they all have to be first.
permit() doesn't use keyword arguments though... This isn't what's actually going on.