Unify method and field symbol spaces on objects

[jclark]

Currently objects have separate symbol spaces for methods and fields.

AFAIR the logic for this was to make the field symbol space similar to records and not have it be polluted with double underscore methods. But

• we no longer have double underscore methods; only init remains as a reserved method name
• the separation causes some problems (Direct access to bound method that preserves annotations #98 and Syntax to allow directly calling a field of function type #257)
• objects are more similar to modules then records, and modules have a single symbol space for functions and variables

Overall it therefore seems better to have a unified symbol space.

With this, #98 is solved simply by allowing field access to be applied to a method: the result will be a closure of the function with self bound to the particular object.

var obj = object {
  int n = 0;
  function get() returns int { n += 1; return n; }
};

var f = obj.get;

Similarly, #257 is solved by making method call syntax when applied to a field of function type call the function.

[jclark]

There are two possible concepts of a method call.

1. A method is that it is a function with a special parameter. The method call syntax is way of providing this parameter.
2. Initialization stores in the object a closure in which self is bound to the object being initialized. Method call is just a field access that retrieves the closure and calls it. From a type perspective, an object method is just a readonly field that contains a function. A method definition is special in a class in that it automatically takes care of initializing the field to a closure.

Concept 2 is attractive because it makes the solutions to #98 and #257 work automatically, without any special rules.

However the approach to isolated in #145 does not work with concept 2 without some additional complexity. We want isolated methods to have access to self in the same way as any other parameter, otherwise it becomes much more burdensome to write isolated methods than isolated functions. This has the following consequence (regardless of whether we use concept 1 or 2). Given:

var obj = object {
  int n = 0;
  isolated function get() returns int { n += 1; return n; }
};

var f = obj.get;

the bound method f is not isolated.

I think this means we do also need the concept of isolated objects as well as isolated functions. For example:

var obj = isolated object {
  private int n = 0;
  isolated function get() returns int { 
    lock {
      n += 1;
      return n; 
    }
  }
};

var f = obj.get;

This would make the type of the bound method f be isolated. We need to figure out exactly what the rules are for isolated objects.