Hi Michael, Many thanks for your reply, I can definitely see your point.
I agree that it makes sense for EMPTY_MAP to have the same logic as Map.of() or unmodifiable(new HashMap()), which means that my suggestion cannot be applied to just EMPTY_MAP... but maybe that’s ok: maybe we can change all of them? If we keep the default implementation for Map.computeIfPresent in EMPTY_MAP, Map.of(), unmodifiableMap, etc., instead of overriding it to throw an exception, then: - For cases where the key isn’t present (regardless of empty or non-empt map), the call will be a safe no-op. - For cases where the key is present, the call will still throw UOE via the implementation of put() I believe this would still respect the spec for Map.computeIfPresent while providing a more forgiving implementation (in the sense that it will avoid throwing an exception when possible). Thoughts? Abraham > On 10 Jun 2019, at 14:27, Michael Rasmussen <michael.rasmus...@roguewave.com> > wrote: > >> If I understand correctly, this class represents an immutable empty map. As >> a result, operations like put or remove have been implemented to throw >> UnsupportedOperationException; this makes sense to me. However, this is >> also the implementation for computeIfPresent, which I believe may be too >> disruptive: the definition of this method says “If the value for the >> specified key is present and non-null, attempts to compute a new mapping >> given the key and its current mapped value.“; for an empty map, this could >> be a safe no-op, instead of an exception. > > The spec for Map.computeIfPresent states that it should throw > UnsupportedOperationException if Map.put is not supported, which is the case > for this map. > The exception is listed as "(optional)" though, for which the docs specify > "may throw an exception or it may succeed, at the option of the > implementation." so it's not entirely clear to me if it would be OK for > computeIfPresent to not throw. > > That being said -- for me it makes more sense that Collections.emptyMap() > follows the same logic as Map.of(), or Collections.unmodifiableMap(new > HashMap<>()) -- and the latter two both throw from computeIfPresent. > > /Michael
