[type-annos-observers] ordering of annotated array brackets

[Michael Ernst]

Alex-

Thanks for the clarification!

>>>> As another example, consider
>>>>
>>>>      @A T @B [] arr1, arr2 @C [];
>>>>
>>>> arr1 should have the same annotations as the elements of arr2.  So,
>>>>
>>>>      @A T @B [] arr2 @C [];
>>>>
>>>> should be equivalent to
>>>>
>>>>      @A T @C [] @B [] arr2;
> 
> I think you're saying: the elements of arr2 should be the same as the elements of arr1.

No, I meant that arr1 (whose type is "@A T @B []") should have the same type as the components of arr2 (whose type is also "@A T @B []", since the type of arr2 is "@A T @C [] @B []").

I think that is consistent with the rest of my message, but I was sloppy in mixing up the JLS's "array component" vs. "array element" terminology.  (I am not fond of that terminology, though I know that's not your fault.)  I think this clears up at least part of the confusion.

My position is that this assignment should type-check for any type MyType:

  MyType arr1, arr2[];
  arr2[7] = arr1;

I think it would be extremely confusing to users (it would violate the principle of least surprise) if this was not the case.  In particular, this assignment should type-check:

  @A T @B [] arr1, arr2 @C [];
  arr2[7] = arr1;


                    -Mike


> Subject: Re: [type-annos-observers] ordering of annotated array brackets
> From: Alex Buckley <alex.buckley at oracle.com>
> To: type-annotations-spec-experts <type-annotations-spec-experts at openjdk.java.net>
> Date: Tue, 04 Mar 2014 15:13:37 -0800
> 
> On 3/3/2014 1:55 PM, Michael Ernst wrote:
>>> So in a field declaration with two declarators, arr1 and arr2:
>>>
>>>   @A T @B [] arr1,    arr2 @C [];
>>>
>>> the extra dimension in the second declarator should not affect the
>>> type or annotations of the first declarator. Yet you seem to be saying
>>> that arr2's extra dimension affects the type of arr1?!
>>
>> I didn't intend to say that.
>>
>> Can you explain how you think I'm saying that arr2's extra dimension
>> affects the type of arr1?
> 
> // Using the JLS ch.10 terminology carefully re: array elements v. array components.
> 
> Consider:
> 
>>>> As another example, consider
>>>>
>>>>      @A T @B [] arr1, arr2 @C [];
>>>>
>>>> arr1 should have the same annotations as the elements of arr2.  So,
>>>>
>>>>      @A T @B [] arr2 @C [];
>>>>
>>>> should be equivalent to
>>>>
>>>>      @A T @C [] @B [] arr2;
> 
> I think you're saying: 1) the elements of arr1 are @B, and 2) the elements of arr2 should be the same as the elements of arr1. I agree with (1) but not (2). I guess (2) is deduced from the principle that:
> 
> "in two declarations that differ only in the number of array levels, the annotations mean the same thing."
> 
> That is, arr1 and arr2 differ only in the number of array levels, so if @B applies to arr1's element type, then @B should apply to arr2's element type, right?
> 
> I disagree where post-identifier brackets are concerned, because I think that adding them should not cause the reader to do gymnastics on the annotated array type. It's simply astonishing that post-identifier [] pairs are inserted _before_ the normal [] pairs. I keep recalling the beauty of:
> 
> @A T   x;
> @A T[] y;
> 
> whereby adding [] doesn't affect anything to the left of []; in that vein, adding @C [] should not affect anything to the left @B [].
> 
> @A T @B [] arr1;
> @A T @B [] arr2 @C [];
> 
> The principle of least surprise is important.
> 
> Alex
> 
>>                      -Mike
>>
>>> Subject: Re: [type-annos-observers] ordering of annotated array brackets
>>> From: Alex Buckley <alex.buckley at oracle.com>
>>> To: type-annotations-spec-experts
>>> <type-annotations-spec-experts at openjdk.java.net>
>>> Date: Tue, 04 Mar 2014 13:47:10 -0800
>>>
>>> On 3/4/2014 9:29 AM, Michael Ernst wrote:
>>>> There was some text in the old specification about this issue.  It was
>>>> commented out in September 2011 for brevity, but not because of
>>>> controversy.
>>>>
>>>> In this (deprecated but legal) syntax, in each component you read
>>>> left-to-right, like this:
>>>>
>>>>      @English String @NonNull [] [] []  arr1,   arr2 @Length(10) []
>>>> [] [];
>>>>      3-------------> 2---------------> 1------------------>
>>>>
>>>> As another example, consider
>>>>
>>>>      @A T @B [] arr1, arr2 @C [];
>>>>
>>>> arr1 should have the same annotations as the elements of arr2.  So,
>>>>
>>>>      @A T @B [] arr2 @C [];
>>>>
>>>> should be equivalent to
>>>>
>>>>      @A T @C [] @B [] arr2;
>>>
>>> I don't understand this at all. Allow me to refer to section 2.2.1 of
>>> java-annotation-design.pdf:
>>>
>>> --
>>> An important property of this syntax is that, in two declarations that
>>> differ only in the number of array levels, the annotations mean the
>>> same thing. For example, var1 has the same annotations as the elements
>>> of arr2:
>>>   @NonNull String var1;
>>>   @NonNull String[] arr2;
>>> because in each case @NonNull refers to the String, not the array.
>>> This consistency is especially important since the two variables may
>>> appear in a single declaration:
>>>   @NonNull String var1, arr2[];
>>> --
>>>
>>> So in a field declaration with two declarators, arr1 and arr2:
>>>
>>>   @A T @B [] arr1,    arr2 @C [];
>>>
>>> the extra dimension in the second declarator should not affect the
>>> type or annotations of the first declarator. Yet you seem to be saying
>>> that arr2's extra dimension affects the type of arr1?!
>>>
>>> Alex