----- Original Message -----
> From: "John R Rose" <jr...@openjdk.java.net>
> To: "core-libs-dev" <core-libs-dev@openjdk.java.net>
> Sent: Tuesday, March 8, 2022 5:55:00 PM
> Subject: Re: RFR: JDK-8282798 java.lang.runtime.Carrier
> On Tue, 8 Mar 2022 15:59:59 GMT, Maurizio Cimadamore <mcimadam...@openjdk.org>
> wrote:
>
>>> We propose to provide a runtime anonymous carrier class object generator;
>>> java.lang.runtime.Carrier. This generator class is designed to share
>>> anonymous
>>> classes when shapes are similar. For example, if several clients require
>>> objects containing two integer fields, then Carrier will ensure that each
>>> client generates carrier objects using the same underlying anonymous class.
>>>
>>> See JBS for details.
>>
>> src/java.base/share/classes/java/lang/runtime/Carrier.java line 48:
>>
>>> 46:
>>> 47: /**
>>> 48: * This class is used to create objects that have number and types of
>>
>> The class javadoc seems a bit on the thin side. I would say something on the
>> fact that the shape of the carrier is determined by a MethodType, etc, and
>> add
>> an example to illustrate basic usage.
>
> Agreed. Also, this class is unusual in that it is not instantiated; like
> `Arrays` or `Collections` it is a (small) bundle of static factories (or are
> they algorithms?). I think as such it should be called `Carriers`.
>
> I'm slightly surprised the MH factories are not factored through a metaobject
> of
> the form
>
> record CarrierBinding(
> MethodType methodType,
> MethodHandle constructor,
> List<Class<?>> componentTypes,
> List<MethodHandle> components)
> { … }
Yes, i've done something very similar
https://github.com/forax/switch-carrier/blob/master/src/main/java/com/github/forax/carrier/java/lang/runtime/Patterns.java#L172
Note that constructor.type() == methodType and constructor.parameterList() ==
componenetTypes,
so the record can be reduced to a tuple (constructor / components).
>
>
> The presupposition here, I suppose, is that carriers will only be used by
> condy
> or similar quasi-statically configured clients, so having the multiple lookups
> through a hidden table is no burden, and the clients can always keep the
> associations correct (between constructors and various component accessors).
>
> **But** if I were to use carriers to manage intermediate structures in (say) a
> serialization package (for instance) I would need to make my own records like
> the above for my own bookkeeping, and I would be slightly miffed that the
> Carrier API insisted on doing a de-novo lookup twice on each MT key (to say
> nothing of me having to create the MT key first).
It depends if you want to use the same carrier for several cases or not.
>
> **And** if I were to use carriers in that way (away from condy), **then** I
> would want to skip the step of building the MethodType, and wish for a factory
> method for CarrierBinding instances that took a plain List<Class>, as well as
> a
> factory method that took the MethodType (which is convenient for condy).
As i said above, constructor.type() == methodType so anyway the MethodType has
to be created.
>
> BTW, it would be normal to give the name `Carrier` (which is a good name BTW)
> to
> the record type that embodies the group of method handles, so `record
> Carrier(…constructor…components…) {…factories…}`.
>
> I suppose stuff like this could be added later. But it's worth considering
> now,
> simply because there is an early decision point between a class named
> `Carrier`
> and a static-only class named `Carriers`.
Rémi
