[lvti] Non-denotable types

Tagir Valeev amaembo at gmail.com
Fri Jul 14 05:15:48 UTC 2017


When thinking about local variable type inference, I noticed that lambda
parameter type inference in Java 8 is sometimes similar. For example, we
can declare the following method:

    static <T> void var(T t, Consumer<? super T> cons) {

Then Java 8 code like this:

   var(theValue, theVariable -> {

Is equivalent to LVTI code like this:

  var theVariable = theValue;

Apparently this does not work for non-denotable types. I checked the
non-denotable types section in [1]: seems that lambda parameter inference
infers to non-denotable type as it described in this section, which already
produces "surprising" results:

    void test(List<?> l1, List<?> l2) {
        var(l1, l3 -> {
            l3 = l2; // error
            l3.add(l3.get(0)); // error

Shouldn't we expect a consistency here? There's already a kind of variables
in Java (lambda parameters) for which non-denotable types are inferred. It
looks strange to me that two kinds of variable inference work in different

With best regards,
Tagir Valeev

[1] http://openjdk.java.net/jeps/286

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