> From: "Brian Goetz" <brian.go...@oracle.com> > To: "Remi Forax" <fo...@univ-mlv.fr> > Cc: "amber-spec-experts" <amber-spec-experts@openjdk.java.net> > Sent: Wednesday, March 30, 2022 2:42:38 AM > Subject: Re: [External] : Re: Declared patterns -- translation and reflection
>> 1/ conceptually there is a mismatch, the syntax introduce names for the >> bindings, but they have no names at that point, bindings only have names >> AFTER >> the pattern matching succeed. > I think you have missed the point here. The names serve the implementation of > the pattern, not the interface -- just as parameter names to methods do. As > you > see in the example, these are effectively blank final locals in the body of > the > pattern, which must be assigned to. (I'd have pointed this out if this were > actually a message on declaring deconstructors, but since the message is on > translation and reflection I didn't want to digress.) >> 2/ sending the value of the binding by name is alien to Java. In Java, >> sending >> values is by the position of the value. > It's not by name. I don't know where you got this idea. >> 3/ the conceptual mismatch also exists at runtime, you need to permute the >> value >> of bindings before creating the carrier because a carrier takes the value of >> the binding by position while the code will takes the value of the bindings >> by >> name (you need the equivalent of MethodHandles.permuteArguments() otherwise >> you >> will see the re-organisation of the code if they are side effects). > It's not by name. I don't know where you got this idea. I think i understand the underlying semantics of the syntax, i'm not 100% confident. You know that it's not about the syntax per se but what the syntax try to communicate to the users. The problem with the proposed syntax is that you invent a new kind of variable, until now, we had local variables and fields (and array cells but those have no name). Your binding is a new kind of variable. It means that - as a user, i need to learn new rules: can i use the value of a binding to compute the value of another one, can i declare a binding final ? can i capture a binding in a lambda/anonymous class ? etc - the JLS needs to artificially grows to cover all these rules - the JVMS needs to be updated, more questions: do we need an attribute LocalBindingTable like we have a LocalVariableTable - tools needs to be updated: how debuggers reflects bindings, is it another tables in the UI ? Do/Can the debugger allows to chain the value of the binding while a user steps into the code, etc All this pain, because you want to name bindings. Rémi
