Jrose: New page: Do we need interface injection, or do ClassValue and invokedynamic do everything we want? Let's gather the use cases. Definitions and design discussion may be found at [[Interface_inject...

2011-07-20T23:07:46Z

New page: Do we need interface injection, or do ClassValue and invokedynamic do everything we want? Let's gather the use cases. Definitions and design discussion may be found at [[Interface_inject...

New page

Do we need interface injection, or do ClassValue and invokedynamic do everything we want?

Let's gather the use cases.

Definitions and design discussion may be found at [[Interface_injection|Tobias Ivarsson's "Case for Interface Injection"]].

== use cases for injecting the supertype *only* ==

In many cases, adding runtime information to arbitrary target classes can best be done with java.lang.ClassValue. The invokedynamic instruction can encode associated operations with this ClassValue.

In some cases, there is a prior commitment or inclination to use Java interfaces and perhaps interface inheritance.

=== Infinite Supertypes ===
Some languages (a) have infinite sets of supertypes, and (b) want to represent their types as Java classes and interfaces. Scala and Fortress are in this category.

Example: Given the way function types work, ()->String is a subtype of ()->Object. Argument type "go backwards", so (String)->void is a *supertype* of (Object)->void. In fact, (Foo)->void is a supertype of (Object->void for every subclass Foo of object! Thus, if a language represents (Object)->void as an interface IFn_Object_V, it may attempt to declare super-interfaces in the classfile of IFn_Object_V, including IFn_String_V, etc. If a new type Foo is loaded, then IFn_Foo_V should be retroactively added to the super-interface list for IFn_Object_V.

Workaround: Have the language use JVM interface subtyping as a first resort, but have its own subtype algorithm (like the JVM's) as a last resort. Same idea for method lookup, if IFn_Foo_V contains Java methods.

== use cases for injecting methods ==

=== Defender methods ===
Defenders are methods which can be added to implementations of interfaces, where the implementation class and the interface are statically related; there is no need to modify a type's supertypes.

== external links ==
;Old Proposal: http://blogs.oracle.com/jrose/entry/interface_injection_in_the_vm

Why Interface Injection - Revision history

Jrose: New page: Do we need interface injection, or do ClassValue and invokedynamic do everything we want? Let's gather the use cases. Definitions and design discussion may be found at [[Interface_inject...