Re: [weld-dev] Proxies.TypeInfo.getSuperInterface() question
Hi,
so I think (I wasn't there at the time so I cannot really remember it :)) the name
`getSuperInterface` or `getSuperClass`on `Proxies.TypeInfo` class comes from the fact that
these method return you a class/interfaces that is a direct superclass for the proxy class
you are creating.
E.g. this is used in places like `ProxyFactory` where you would use
`typeInfo.getSuperInterface()` as a means of saying "give me what will be the direct
superclass of the proxy I am now creating".
You want your proxies to be based on the most concrete type of the bean for apparent
reasons - you want the proxy to match all possible injection points, so it has to fit into
all types, which is exactly what the most specific type will do.
So in your 2 interface scenario with Square and Rectangle, you will always want to base
proxy on Square so that the proxy has both types; therefore these methods will return you
`Square` - a super interface for the proxy you are doing.
That's the way I read the code at least, your mileage may vary :)
Matej
----- Original Message -----
From: "Laird Nelson" <ljnelson(a)gmail.com>
To: weld-dev(a)lists.jboss.org
Sent: Friday, March 6, 2020 2:51:02 AM
Subject: [weld-dev] Proxies.TypeInfo.getSuperInterface() question
I am reading Weld code to understand deeply how proxies work.
While doing this, I ran across the Proxies.TypeInfo class. It has a method
called getSuperInterface() .
This method iterates over a set of interfaces and selects the most specific
one (somewhat surprisingly to me; I would have expected the most general
one).
The method is very short so here it is in its entirety, reformatted:
public Class<?> getSuperInterface() {
if (interfaces.isEmpty()) {
return null;
}
Iterator<Class<?>> it = interfaces.iterator();
Class<?> superclass = it.next();
while (it.hasNext()) {
Class<?> clazz = it.next();
if (superclass.isAssignableFrom(clazz)) { // XXX Is this backwards?
superclass = clazz;
}
}
return superclass;
}
For example, if there are exactly two interfaces in the set, Square.class and
Rectangle.class , and Square extends Rectangle , it would seem that
Square.class will be selected.
(My reading: Pretend Square.class is the first item in the iterator. It gets
assigned to superclass . Then clazz gets the next (and last) item,
Rectangle.class . Then we check to see if (effectively)
Square.class.isAssignableFrom(Rectangle.class) , which will return false .
So superclass remains Square.class and is returned.
(Or pretend that Rectangle.class was the first item in the iterator. It gets
assigned to superclass . Then clazz gets Square.class . Then we check to see
if Rectangle.class.isAssignableFrom(Square.class) , which returns true , so
superclass gets reassigned to Square.class , and is then returned. Hence
Square.class , the most specific subtype in the set, is returned in both
cases.)
The reason this surprised me is the name of this method implies that it
should select the most general , e.g. Rectangle.class in my example. That's
usually what "super" means.
See
https://github.com/weld/core/blob/10a1d11af8c815a2a4a8fc5a4061698215e602b...
.
Is that line "backwards"? Or is it just a badly-named method (should it have
been named getMostSpecificInterface() )? Or…?
I understand this code is old and works and so my apologies if I'm being
stupid in some way. I just like to understand things.
Best,
Laird
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