A suggestion: Map.checkAndGet

[Mike Duigou]

Unfortunately such a method would introduce non-atomic behaviour for synchronized maps so we can't add it.

Mike

On Oct 30 2012, at 08:25 , Boaz Nahum wrote:

> The pattern
> map.containsKey(k) ? map.get() : othervAlue
> (walks on tree twice)
> 
> repeats itself so many times, as in Mappers:
> 
> public static <T, U> Mapper<T, U> forMap(Map<? super T, ? extends U> map,
> U defaultValue) {
>        Objects.requireNonNull(map);
> 
>        return t -> map.containsKey(t) ? map.get(t) : defaultValue;
> }
> 
> 
> Now that we have 'default methods', we can add to Map:
> 
> NullableOptional<V> checkAndget(K key) default {
> 
>        if (containsKey(key)) {
>            return new NullableOptional<>(get(key));
>        } else {
>            return NullableOptional.empty();
>        }
>    }
> 
> **and** implement it in Map implementation in such way that will walk on
> tree only once.
> (Assume creating instance of NullableOptional is more  efficient )
> 
> forMap becomes:
> 
> public static <T, U> Mapper<T, U> forMap(MyMap<? super T, ? extends U> map,
> U defaultValue) {
>        Objects.requireNonNull(map);
> 
> 
>        return t -> {
>            NullableOptional<? extends U> o = map.checkAndget(t);
>            return o.isPresent() ? o.get() : defaultValue;
>            //return o.orElse(defaultValue);
>        };
>    }
>