> Contrast Java with Ruby or C#. There, the clients don't need to know whether they're accessing a member var or calling a method to get/set a property, NOR SHOULD THEY.

Others have noted that in many contexts in C# there is a difference, so clients do need to know.

As far as Ruby, clients definitely need to know, its just that since public fields can't happen in Ruby, its always method-based access for the normal cases.

Both of these lines are always calling a method on "obj" in Ruby:

  foo = obj.a  # equivalent to foo = obj.a() 
  obj.a = foo  # equivalent to obj.a=(foo)

While these are using instance var (the closest thing to a "field" in Ruby) access:

  foo = obj.instance_variable_get :@a
  obj.instance_variable_set :@a, foo
  foo = obj.instance_eval { @a }
  obj.instance_exec { @a = foo }

There's no common syntax like C#-style properties that unifies field-based and method-based access, so Ruby is sort of the extreme opposite of attempts to have "properties" that make method-based access look the same as field-based access in the same language, even though its method syntax can make method-based access in Ruby look like field-based access in a completely different language.