[Grace-core] The no shadowing rule

[Andrew P Black]

Thinking about this some more, we have to allow re-use of methods names, but can prohibit re-use of other names.  That makes for a simple rule.

The key, though, is to remember what makes a method.  Obviously, things declared using the method keyword are methods.  But every def inside an object (which includes inside a module, class or a factory method) also makes a method (possibly confidential, but still a method), and every var makes two methods.  A class declaration is equivalent to a def, so it makes a method, too (and the spec is silent on whether a class is public or confidential by default — I added a note that we need to fix this).

Parameters never make methods.  Names defined in an import statement make (confidential by default) methods in the module object.

So, my program 3

class y.new { … }

class z.new {
	method y { … }
}

should be OK, because y is a method in the module object, and also in the z.new object, and it's OK to have multiple objects with the same method names — indeed, it's the key to the power of OO.   In contrast, Programs 1 & 2 both reuse the name of a parameter for a method.
The parameter thus becomes inaccessible — there seems no reason to allow this, and it is always possible to rename the parameter, with no effect on any client.

	Andrew

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