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From MG <mg...@arscreat.com>
Subject Re: Making @Immutable a meta-annotation
Date Mon, 15 Jan 2018 14:56:49 GMT
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)).

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 ?

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").

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...

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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