Filip S. Adamsen wrote:
Hi,
As far as I know it's very difficult - if not impossible - for
Tapestry to support generics in method parameters because of the way
generics are implemented in Java (type erasure).
A lot of type information is still available through reflection.
Assuming concrete component classes do not have generic parameters (they
have all super class type parameters fulfilled), all type information
will be available at runtime. You can’t deduct the “unerased” types from
the instances, but you can deduct part of it from the classes.
For example, here is my own “TypeOracle” that is used in my code for
following the property path (finding the “real”, “unerased” type of the
next property in the property path):
http://nanorm.googlecode.com/svn/trunk/src/main/java/com/google/code/nanorm/internal/introspect/TypeOracle.java
It just requires a lot of careful work.
For example, here is the deduction steps for base onActivate that could
be made at runtime:
1) We have SubClass with all types known. We know that base class is
actually ParameterizedType with raw class “SuperClass” and first actual
type parameter “Bar” (SubClass.class.getGenericSuperclass()).
2) Looking at the onActivate(E param) method we see that its first
parameter is some type variable (method.getGenericParameterTypes()).
3) We see that this type variable is equals to the first type variable
of the “SuperClass” (array SuperClass.getTypeParameters()).
4) Since this first parameter is substituted by “Bar” (see 1)), we can
deduct that this method has first parameter of type “Bar”.
5) Now we can see that our method onActivate(Bar bar) actually overrides
base method onActivate(E e) (which at runtime has type onActivate(Foo
foo). So we don’t need to invoke it.
Something like this.
--
WBR,
Ivan S. Dubrov
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