Description Markus Keller 2005-07-07 13:39:06 EDT

I20050627-1435 (3.1)

We have a problem calculating the correct type declaration of variables to which
an expression with a type of the form A<B<capture-of-?>> should be assigned.

Such an expression cannot be assigned to a variable of type A<B<?>>, since the
type arguments B<capture-of-?> and B<?> are not equal.
An A<B<capture-of-?>> can only be assigned to a variable of type A<? extends B<?>>.

Example: Assigning Collections.nCopies(2, list) to a new local results in a
compile error here:

void assignToNewLocal(ArrayList<?> list) {
    List<ArrayList<?>> dups= Collections.nCopies(2, list); // illegal
    List<? extends ArrayList<?>> extDups= Collections.nCopies(2, list); //legal
}

The javadoc of ImportRewrite#addImport(ITypeBinding, AST) already tells: "The
returned type node represents a type to which the type binding can be assigned
or casted to.". Easiest would be if the ImportRewrite could also handle this
situation correctly. I.e. it should replace the pattern 'B<capture-of-?>' by '?
extends B<?>' if it occurs in a type argument list. If 'B<capture-of-?>' appears
as top-level type, it should be replaced by 'B<?>' (works already).


Here are some more examples:

void extractLocal(HashMap<String, ? extends Number> nameToNumber) {
    // legal:
    Entry<String, ? extends Number> item=
        nameToNumber.entrySet().iterator().next();

    // illegal:
    Set<Entry> set= nameToNumber.entrySet();
    Set<Entry<String, ? extends Number>> entrySet= nameToNumber.entrySet();

    // legal:
    Set<? extends Entry> extSet= nameToNumber.entrySet();
    Set<? extends Entry<String, ? extends Number>> extEntrySet=
        nameToNumber.entrySet();
}