I have just pushed code to mlvm/{langtools,jdk} which reflects the following
syntax change for method handle invocation:
T x = mh.<T>invokeExact(...);
=>
T x = (T) mh.invokeExact(...);
and:
{mh.<void>invokeExact(...);}
=>
{mh.invokeExact(...);}
In other words, we are replacing fake type parameters (void? int?) with real
casts, as a better notation for the intended type of the MH invocation.
The old format still works temporarily in a compatibility mode, unless you turn
off the compatibility mode. If you want to compile your code in the strict
mode, to catch old usages, compile like this:
$ javac -XDallowTransitionalJSR292=no
At some point before JSR 292 PFD, the default will change, and the flag will be
required to support the type parameter syntax:
$ javac -XDallowTransitionalJSR292=yes
Warning: The treatment of the "<void>" case is potentially a code-breaking
change. To avoid the breakage, you have to force your invocation statement to
produce an explicit value:
{mh.invokeExact(...);}
=>
{Object junk = mh.invokeExact(...);}
See the paragraph in JLS 14.8 "Expression Statements" containing the phrase
"such a trick" for discussion of this corner of the language.
Updated language rules are documented here:
http://wikis.sun.com/display/mlvm/InterfaceDynamic
These rules are provisional, but I expect them to replace the old ones, which
did more violence to the language.
Best wishes,
-- John
P.S. Similar changes apply to InvokeDynamic, which also has a statically
checked requirement for an enclosing @BootstrapMethod annotation. If you have
been (a) writing InvokeDynamic invocation syntax in Java source code, or (b)
spinning invokedynamic bytecodes, the recent addition of local bootstrap
methods is a change you'll need to catch up with soon.
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