[jira] [Commented] (GROOVY-10944) Inconsistency with getAt between List and other Iterables

["Paul King (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/GROOVY-10944?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17692931#comment-17692931 ] 

Paul King commented on GROOVY-10944:
------------------------------------

We would likely make all cases return {{ArrayIndexOutOfBoundsException}}. The negative index value access is a convenience for getting values from the right-hand end of the list. In previous discussions it was deemed too magical to also combine that with other behaviors. In particular, {{putAt}} with an index value outside the size can grow a list but growing in the negative direction doesn't make any sense. The Javadoc certainly has scope for clarification.

> Inconsistency with getAt between List and other Iterables
> ---------------------------------------------------------
>
>                 Key: GROOVY-10944
>                 URL: https://issues.apache.org/jira/browse/GROOVY-10944
>             Project: Groovy
>          Issue Type: Bug
>          Components: groovy-jdk
>    Affects Versions: 4.0.9
>            Reporter: M. Justin
>            Priority: Minor
>
> I noticed a difference in behavior between how {{getAt(int index)}} functions for {{List}} and other implementations of {{{}Iterable{}}}.  Namely, non-{{{}List{}}} {{{}Iterable{}}}s will return {{null}} for negative values outside of the range of items, whereas {{List}} will throw {{{}ArrayIndexOutOfBoundsException{}}}.
> {code}
> def tryPrint(Iterable o, int index) {
>   try {
>       println(o[index])
>   } catch (Exception e) {
>       println(e.getClass().simpleName)
>   }
> }
> List<String> strings = ['A', 'B', 'C']
> tryPrint(strings as Set, -4) // null
> tryPrint(strings as List, -4) // ArrayIndexOutOfBoundsException
> tryPrint(Collections.unmodifiableCollection(strings), -4) // null
> {code}
> The documentation for {{Iterable.getAt}} seems to indicate that null should be returned if there value is out of range (there is "no corresponding value"):
> {quote}*Returns:*
> the value at the given index (after normalisation) or null if no corresponding value was found
> {quote}
> The documentation for List.getAt makes no such claims:
> {quote}*Returns:*
> the value at the given index
> {quote}
> It seems undesirable for the subclass method to throw an exception where the superclass method does not.  It seems extra undesirable given that the difference is not documented.
> Note that both {{List}} and non-{{List}} {{{}Iterable{}}}s will return {{null}} for positive values outside of the range of items:
> {code}
> tryPrint(strings as Set, 4) // null
> tryPrint(strings as List, 4) // null
> tryPrint(Collections.unmodifiableCollection(strings), 4) // null
> {code}
> h2. Expected behavior:
> I would expect consistent behavior between {{List}} and non-{{{}List{}}} {{{}Iterable{}}}s with regard to this method, given that there's nothing special about {{List}} that would appear to warrant this difference.
> It feels like both should return {{null}} when the index is out of range (positive or negative).  But having both throw the exception in that case would be reasonable, if less convenient.
> h2. Similar past issues:
> There are two "won't fix" issues regarding the inconsistency between positive and negative out-of-bounds behavior of {{{}List{}}}:
>  * GROOVY-1286
>  * GROOVY-4652
> However, these were concerned with the inconsistency within {{List}} itself.  As this ticket involves the inconsistency between {{List}} and non-{{{}List{}}} {{{}Iterable{}}}s, and not the between positive/negative index behavior, I would argue it's a different problem than these two existing issues.



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