Since Ruby 3, the automatic coercion of keywords to a hash—the second example underneath "Passing Hash to Functions" in this post—is considered a legacy style and is generally frowned upon in new code. That is to say, code like the second call to `foo` here:
One of the strongest arguments for avoiding this sugar is that it makes the code more brittle in the face of future changes. In particular, in the example above, if we add a new keyword argument to `foo`, then any call which omitted the curly braces will break, while calls which used them will keep working fine:
# added a new keyword arg here
def foo(kwargs = {}, frob: false)
kwargs
end
foo({k: 1}) # still ok: `frob` defaults to false
foo(k: 1) # ArgumentError: no keyword: :k
That's kind of the point of default values, though. If you wanted to make a change to the method and you want it to break to alert you to all the calls, then you can add a keyword without adding a default value for it.