On Mon, 30 Nov 2020 13:52:17 GMT, Pavel Rappo <pra...@openjdk.org> wrote:
>> @pavelrappo Please see my updated CSR below. Thanks.
>>
>> # Map::compute should have the implementation requirement match its default
>> implementation
>>
>> ## Summary
>>
>> The implementation requirement of Map::compute does not match its default
>> implementation. Besides, it has some other minor issues. We should fix it.
>>
>> ## Problem
>>
>> The documentation of the implementation requirements for Map::compute has
>> the following problems:
>> 1. It doesn't match its default implementation.
>> 1. It lacks of the return statements for most of the if-else cases.
>> 1. The indents are 3 spaces, while the convention is 4 spaces.
>> 1. The if-else is overly complicated and can be simplified.
>> 1. The surrounding prose contains incorrect statements.
>>
>> ## Solution
>>
>> Rewrite the documentation of Map::compute to match its default
>> implementation and solve the above mentioned problems.
>>
>> ## Specification
>>
>> diff --git a/src/java.base/share/classes/java/util/Map.java
>> b/src/java.base/share/classes/java/util/Map.java
>> index b1de34b42a5..b30e3979259 100644
>> --- a/src/java.base/share/classes/java/util/Map.java
>> +++ b/src/java.base/share/classes/java/util/Map.java
>> @@ -1107,23 +1107,17 @@ public interface Map<K, V> {
>> *
>> * @implSpec
>> * The default implementation is equivalent to performing the following
>> - * steps for this {@code map}, then returning the current value or
>> - * {@code null} if absent:
>> + * steps for this {@code map}:
>> *
>> * <pre> {@code
>> * V oldValue = map.get(key);
>> * V newValue = remappingFunction.apply(key, oldValue);
>> - * if (oldValue != null) {
>> - * if (newValue != null)
>> - * map.put(key, newValue);
>> - * else
>> - * map.remove(key);
>> - * } else {
>> - * if (newValue != null)
>> - * map.put(key, newValue);
>> - * else
>> - * return null;
>> + * if (newValue != null) {
>> + * map.put(key, newValue);
>> + * } else if (oldValue != null || map.containsKey(key)) {
>> + * map.remove(key);
>> * }
>> + * return newValue;
>> * }</pre>
>> *
>> * <p>The default implementation makes no guarantees about detecting if
>> the
>
> @johnlinp, thanks for updating the CSR draft; it is much better now.
>
> @stuart-marks, I think we could further improve this snippet. This `if`
> statement seems to use an optimization:
>
> if (oldValue != null || map.containsKey(key))
>
> I don't think we should include an optimization into the specification unless
> that optimization also improves readability. Is this the case here? Could
> this be better?
>
> if (map.containsKey(key))
I would even go as far as to rewrite that snippet like this:
if (newValue == null) {
remove(key);
} else {
put(key, newValue);
}
return newValue;
This rewrite is possible thanks to the following properties of
`Map.remove(Object key)`:
1. A call with an unmapped `key` has no effect.
2. A call with a mapped `key` has the same semantics regardless of the value
that this key is mapped to.
In particular, (2) covers `null` values.
To me, this rewrite reads better; however, I understand that readability is
subjective and that snippets used in `@implSpec` might be subject to additional
requirements.
-------------
PR: https://git.openjdk.java.net/jdk/pull/714
