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From MG <mg...@arscreat.com>
Subject Re: Making @Immutable a meta-annotation
Date Tue, 16 Jan 2018 23:54:43 GMT
Hmmm.... If the argument for naming the marker annotation 
@KnownImmutable was that the existing parameters have similar names (and 
cannot be changed) then it seems to me the "KnownImmutable" name choice 
was pretty immutable to begin with...

Apart from that, there is still the inconsistency what @KnownImmutable  
really expresses:

  * Class that carries @KnownImmutable is "fully immutable": When a
    developer puts the annotation on a class
  * Class that carries @KnownImmutable is "bse immutable" (i.e. no
    defense-copying ctors etc): When being put by the Groovy compiler on
    a class after having applied @ImmutableBase transformations to it.

The way it looks to me you are trying to express two different things 
through the same annotation - but to have a clean design you would need 
two seperate annotations. Maybe that is also why you do not like any of 
my alternatives, because you are looking for one name that expresses 
both use cases - and that does not exist, because the use cases differ (?)

I am still convinced that while knownUmmutable semi-works as a parameter 
name inside of @Immutable (I would have picked guaranteed here also), 
that does not mean it is a good choice for the annotation name. But as I 
said, if you are convinced that one requires the other, this discussion 
is mute anyway...


On 16.01.2018 01:56, Paul King wrote:
> Explanations below.
>
> On Tue, Jan 16, 2018 at 12:56 AM, MG <mgbiz@arscreat.com 
> <mailto:mgbiz@arscreat.com>> wrote:
>
>     Hi Paul,
>
>     1) for me, if you have to explain a name better, then it is
>     already a bad name. Intuitively suggesting the correct
>     interpretation to another developer, without requiring him to
>     thoroughly read through the documentation, is the art of picking
>     good names (which imho Groovy overall does a good job at).
>     With regards to @KnownImmutable, "someone (the compiler or the
>     developer) knows" is even more confusing. If it is in fact
>     irrelevant who knows it, why is there a "Known" in the name in the
>     first place ? And why is therefore e.g. @IsImmutable not a better
>     name (it could also carry a parameter which can be true or false,
>     with false allowing a developer to express that a class is
>     definitely not immutable (even if it might look that way on first
>     glance; e.g. effectively blocking or issuing a warning in certain
>     parallel execution scenarios)).
>
>
> We have since the introduction of @Immutable used the knownImmutable 
> and knownImmutableClasses annotation attributes and people seem to 
> grok what they mean. This is a very similar use case. I think it would 
> be hard to justify renaming @KnownImmutable without renaming the 
> annotation attributes as well.
>
>     2) There seems to be a contradiction in your statements: You say
>     that "Once @ImmutableBase (or whatever name) processing has
>     finished its checks, it can then vouch for the class and puts the
>     marker interface [@KnownImmutable] "rubber stamp" on it", but
>     further down you say that "These changes [that @ImmutableBase
>     applies] alone don't guarantee immutability.". Is it a "known
>     immutable" after @ImmutableBase has done its thing, or not ?
>
>
> Only after all transformations have completed it is guaranteed (see 
> below).
>
>     3) If I did not miss something the new @Immutable meta annotation
>     is made up of the following annotations:
>     @ImmutableBase
>     @KnownImmutable
>     @ToString
>     @EqualsAndHashCode
>     @MapConstructor
>     @TupleConstructor
>
>     How is any of the last four necessary for a class to be immutable
>     ? Immutability to me means, that the state of the class cannot be
>     changed after it has been created. How are @ToString,
>     @EqualsAndHashCode, @MapConstructor, and @TupleConstructor helping
>     with this ?
>     At least one ctor to initialize the class fields is basically
>     necessary to make this a practically usable immutable class, yes,
>     but @IsImmutable it must be after @ImmutableBase does its job, or
>     it will not be immutable in the end. All the other annotations are
>     just icing on the cake (see "@Immutable should be named
>     @ImmutableCanonical").
>
>
> @MapConstructor and @TupleConstructor do different things if they find 
> the @KnownImmutable marker interface on the class they are processing 
> (defensive copy in/clone/wrap etc.) which is needed for immutable 
> classes. We could have used an additional annotation attribute 
> (makeImmutable = true) or something but the marker interface is useful 
> in its own right and it seems sensible to not duplicate the 
> information it conveys. Besides we'd have to choose a name for 
> "makeImmutable" and again since it's only part of the immutable story 
> good naming would be hard.
>
>     If you keep @ImmutableBase, at least consider replacing
>     @KnownImmutable with @GuaranteedImmutableTag or
>     @GuaranteedImmutableMarker ? The "Tag" or "Marker" postfix at
>     least expresses that this annotation just tags the class as having
>     certain properties, and that this is a general fact, and not only
>     known to developers or compilers in the know...
>
>
> Marker interfaces are commonplace within the Java world and we don't 
> name them as such. It's not CloneableTag or SerializableMarker. I 
> think adding such a suffix would be confusing.
>
>     I hope I do not completely miss your point, but this is how it
>     looks to me from what I read :-),
>     Cheers,
>     mg
>
>
>
>     On 15.01.2018 14:08, Paul King wrote:
>>
>>     Response below.
>>
>>     On Sun, Jan 14, 2018 at 6:11 AM, MG <mgbiz@arscreat.com
>>     <mailto:mgbiz@arscreat.com>> wrote:
>>
>>         Hi Paul,
>>
>>         now I get where you are coming from with @KnownImmutable. I
>>         agree with splitting the two concepts: Flexible & elegant :-)
>>
>>         Transferring the parameter name knownImmutables (which exists
>>         inside the @Immutable context) to the annotation name
>>         KnownImmutable (which has no such context) still does not
>>         work for me, though.
>>         In addition having @Immutable = @KnownImmutable +
>>         @ImmutableBase violates the definition you give for
>>         @KnownImmutable, because either the class is "known to be
>>         immutable" = "immutable by implementation by the developer",
>>         or it becomes immutable through @ImmutableBase & Groovy...
>>
>>
>>     Well that is perhaps an indication that it needs to be explained
>>     better rather than necessarily a bad name. I'll try again. It
>>     just means that someone (the compiler or the developer) knows
>>     that it is immutable. If that marker interface is on the class
>>     there is no need to look further inside the class, you can assume
>>     it is vouched for as immutable. Once @ImmutableBase (or whatever
>>     name) processing has finished its checks, it can then vouch for
>>     the class and puts the marker interface "rubber stamp" on it.
>>
>>         What do you think about:
>>         @IsImmutable
>>         @ImmutableContract
>>         @GuaranteedImmutable
>>         instead
>>         ?
>>
>>         Thinking about this some more, still don't like
>>         @ImmutableBase. Sounds too much like a base class to me - and
>>         what would be the "base" functionality of being immutable ?
>>         Something either is immutable, or not (@ImmutableCore also
>>         fails in this regard ;-) ).
>>         So still would prefer @ImmutableOnly o.s. ..
>>
>>
>>     @ImmutableOnly indicates that it is somehow immutable at that
>>     point - it isn't really a finished immutable class until all the
>>     other related transforms have done their thing. Perhaps it is
>>     useful to reiterate what it does. It does a whole pile of
>>     validation (you can't have public fields, you can't have certain
>>     annotation attributes on some of the other annotations that
>>     wouldn't make sense for an immutable object, you can't have your
>>     own constructors, it can't be applied on interfaces, it checks
>>     spelling of property names referenced in annotation attributes)
>>     plus some preliminary changes (makes class final, ensures
>>     properties have a final private backing field and a getter but no
>>     setter, makes a copyWith constructor if needed). These changes
>>     alone don't guarantee immutability. Would you prefer
>>     @ImmutablePrelim?
>>
>>         Cheers,
>>         mg
>>
>>
>>         -------- Ursprüngliche Nachricht --------
>>         Von: Paul King <paulk@asert.com.au> <mailto:paulk@asert.com.au>
>>         Datum: 13.01.18 13:17 (GMT+01:00)
>>         An: MG <mgbiz@arscreat.com> <mailto:mgbiz@arscreat.com>
>>         Betreff: Re: Making @Immutable a meta-annotation
>>
>>         I should have explained the @KnownImmutable idea a bit more.
>>         I guess I was thinking about several possibilities for that
>>         in parallel. What I really think is the way to go though is
>>         to split out the two different aspects that I was trying to
>>         capture. One is triggering the AST transformation, the other
>>         is a runtime marker of immutability. With that in mind I'd
>>         suggest the following:
>>
>>         @KnownImmutable will be a marker interface and nothing more.
>>         Any class having that annotation will be deemed immutable.
>>         E.g. if I write my own Address class and I know it's
>>         immutable I can mark it as such:
>>
>>         @KnownImmutable
>>         class Address {
>>           Address(String value) { this.value = value }
>>           final String value
>>         }
>>
>>         Now if I have:
>>
>>         @Immutable
>>         class Person {
>>           String name
>>           Address address
>>         }
>>
>>         Then the processing associated with @Immutable won't complain
>>         about a potentially mutable "Address" field.
>>
>>         Then we can just leave @ImmutableBase (or similar) as the AST
>>         transform to kick off the initial processing needed for
>>         immutable classes.
>>         The @Immutable annotation collector would be replaced by the
>>         constructor annotations, ToString, EqualsAndHashcode and both
>>         ImmutableBase and KnownImmutable.
>>         The name KnownImmutable matches existing functionality. Two
>>         alternatives to annotating Address with KnownImmutable that
>>         already exist would be using the following annotation
>>         attributes on @Immutable:
>>         @Immutable(knownImmutableClasses=[Address]) or
>>         @Immutable(knownImmutables=[address]).
>>
>>         Cheers, Paul.
>>
>>
>>
>>         On Sat, Jan 13, 2018 at 1:43 PM, MG <mgbiz@arscreat.com
>>         <mailto:mgbiz@arscreat.com>> wrote:
>>
>>             Hi Paul,
>>
>>             I think the core of the problem is, that @Immutable as a
>>             meta-annotation woud be better off being called something
>>             along the line of @ImmutableCanonical (see: If you do no
>>             need the immutability, use @Canonical), since it does not
>>             solely supply immutability support - then it would be
>>             natural to call the actual core immutability annotation
>>             just "Immutable".
>>
>>             That is probably off the table, since it would be a
>>             breaking change - so we are stuck with the problem of
>>             naming the immutability annotation part something else.
>>
>>             @ImmutableClass would imply to me that the "Class" part
>>             carries some meaning, which I feel it does not, since
>>             a) "Class" could be postfixed to any annotation name that
>>             applies to classes
>>             b) The meta-annotation should accordingly also be called
>>             "ImmutableClass"
>>             Because of that I find postfixing "Immutable" with
>>             "Class" just confusing. It also is not intuitive to me,
>>             which annotation does only supply the core, and which
>>             supplies the extended (canonical) functionality...
>>
>>             I do not understand where you are going with
>>             @KnownImmutable (known to whom ?-) To me this seems less
>>             intuitive/more confusing than @ImmutableClass...).
>>
>>             @ImmutableCore is similar to @ImmutableBase (because I
>>             intentionally based it on it :-) ), but different in the
>>             sense that it imho expresses the semantics of the
>>             annotation: Making the object purely immutable-only,
>>             without any constructors, toString functionality, etc.
>>
>>             How about:
>>             @ImmutableOnly
>>             @PureImmutable
>>             @ModificationProtected
>>
>>             @Locked
>>             @Frozen
>>
>>             @Unchangeable
>>             @Changeless
>>
>>             @InitOnly
>>             @InitializeOnly
>>
>>             @Constant
>>             @Const
>>
>>             @NonModifieable
>>             @NonChangeable
>>
>>             ?
>>             mg
>>
>>
>>
>>             On 12.01.2018 08:01, Paul King wrote:
>>>             @ImmutableCore is similar to @ImmutableBase - probably
>>>             okay but I don't think ideal. Another alternative would
>>>             be @ImmutableInfo or have an explicit marker interface
>>>             with a different package, e.g.
>>>             groovy.transform.marker.Immutable but that might cause
>>>             IDE completion headaches. Perhaps @KnownImmutable as a
>>>             straight marker interface might be the way to go - then
>>>             it could be used explicitly on manually created
>>>             immutable classes and avoid the need to use the
>>>             knownImmutableClasses/knownImmutables annotation
>>>             attributes for that case.
>>>
>>>             Cheers, Paul.
>>>
>>>             On Thu, Jan 11, 2018 at 9:34 PM, mg <mgbiz@arscreat.com
>>>             <mailto:mgbiz@arscreat.com>> wrote:
>>>
>>>                 Hi Paul,
>>>
>>>                 great to make @Immutable more fine granular /
>>>                 flexible :-)
>>>
>>>                 what about
>>>                 @ImmutabilityChecked
>>>                 or
>>>                 @ImmutableCore
>>>                 instead of @ImmutableClass ?
>>>
>>>                 Cheers
>>>                 mg
>>>
>>>                 -------- Ursprüngliche Nachricht --------
>>>                 Von: Paul King <paulk@asert.com.au
>>>                 <mailto:paulk@asert.com.au>>
>>>                 Datum: 11.01.18 08:07 (GMT+01:00)
>>>                 An: dev@groovy.apache.org
>>>                 <mailto:dev@groovy.apache.org>
>>>                 Betreff: Making @Immutable a meta-annotation
>>>
>>>
>>>                 There has been discussion on and off about making
>>>                 @Immutable a meta-annotation (annotation collector)
>>>                 in much the same way as @Canonical was re-vamped.
>>>                 (This is for 2.5+).
>>>
>>>                 I have a preliminary PR which does this:
>>>                 https://github.com/apache/groovy/pull/653
>>>                 <https://github.com/apache/groovy/pull/653>
>>>
>>>                 Preliminary because it still needs a bit of
>>>                 refactoring to reduce some duplication of code that
>>>                 exists between the normal and immutable map and
>>>                 tuple constructors. I still need to do this but that
>>>                 can happen transparently behind the scenes as an
>>>                 implementation detail if we don't finish it straight
>>>                 away. As well as reducing duplication, the pending
>>>                 refactoring will enable things like the pre and post
>>>                 options for MapConstructor and TupleConstructor
>>>                 which aren't currently working.
>>>
>>>                 I am keen on any feedback at this point. In
>>>                 particular, while most of the functionality is
>>>                 pushed off into the collected
>>>                 annotations/transforms, I ended up with some left
>>>                 over checks which I kept in an annotation currently
>>>                 called @ImmutableClass. I tried various names for
>>>                 this class, e.g. @ImmutableBase and @ImmutableCheck
>>>                 but finally settled on @ImmutableClass since the
>>>                 annotation causes the preliminary checks to be
>>>                 performed but also acts as a marker interface for
>>>                 the MapConstructor and TupleConstructor transforms
>>>                 to do the alternate code needed for immutability and
>>>                 to indicate that a class is immutable when it might
>>>                 itself be a property of another immutable class. Let
>>>                 me know if you can think of a better name or have
>>>                 any other feedback.
>>>
>>>                 Cheers, Paul.
>>>
>>>
>>
>>
>>
>
>


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