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From Stuart Monteith <>
Subject Lists - not useful?
Date Fri, 09 Oct 2009 10:36:19 GMT
    Steve and I have been discussing what to do about lists.

The issues I have with lists are:

1. They provide far more operations that are useful to us, or are desirable for us to implement.
For example:
	. any method that modifies a list.

2. The indices aren't useful. Usually knowing that an object is the nth object in the List
is of no consequence - that relationship to it's peers is normally not terribly important.
What is important is the ID of the object and being able to retrieve that object by its ID.

3. As well as IDs, there are other attributes to search on.

For instance, 

Here are my initial thoughts:

public interface JavaRuntime {
	ResultSet<JavaObject> getAllObjects();
	ResultSet<JavaClass> getAllClasses();


public interface ResultSet<T> {
	// Return a subset of type <T> based on the "filter" string
	// an XPath query.
	ResultSet<T> filterSet(String filter);

	// Reduce this result set using the filter passed.
	void applyFilter(String filter);

	// Return an iterator over the 
	Iterator<T> iterate();

	// Run a query on the string.
	ResultSet<?> query(String filter);

Using this you could do:
	ResultSet<JavaObject> objs = runtime.getAllObjects();
	ResultSet<JavaObject> strings = objs.filterSet("@class[name='java/lang/String']");
To retrieve all of the objects that are instances of String.

Alternatively, you could do:

	ResultSet<JavaObject> strings = runtime.getAllObjects().applyFilter("@class[name='java/lang/String']");

The strings could then be iterated over using the iterator:
	for(JavaObject string : strings.iterator()) {

The filters, I would expect, would have two axes.

For objects:
	a/b - b would be a field
	a@b - b would be an attribute we've added.
		. class - the object's class
		. superclass - the object's superclass.

For classes:
	a/b - b would be a static field
	a@b - b would be an attribute of the class.

For arrays:
	a@b - b would be an attribute
	a[10] - would be the tenth element.

Of course, while a filter is useful, I don't think it's entirely appropriate to use XPath,
which is more appropriate for querying.

Of course, you lose type safety, which is to be expected as a query is in just a string.

For example, to return all of the classes that are strings (in an odd and artifical manner):
	ResultSet<JavaObject> objs = runtime.getAllObjects();

	ResultSet<JavaClass> stringClasses = objs.query("[@class/name='java/lang/String']");

Of course, the question is, how many JavaClasses would be in the result set? There should
be only one in a given runtime.


Stuart Monteith

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