Optional.transformToNullable #1171
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Original comment posted by lowasser@google.com on 2012-10-16 at 03:51 PM More workarounds potentially worth mentioning: Optional.fromNullable(function.apply(value.orNull()); Alternately, users could just write a simple transformNullable(Optional, Function) method themselves. Should we maybe try to search within Google for potential users? Labels: |
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Original comment posted by kak@google.com on 2013-08-22 at 10:50 PM (No comment entered for this change.) Status: |
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Original comment posted by tomas.za...@intelis.cz on 2014-02-13 at 09:02 AM Just note: in JDK8's Optional.map the transformation of null result into empty() is automatic. |
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Original comment posted by jens.ran...@tink.se on 2014-07-09 at 12:36 PM In reply to lowas/#1: The issue with your proposal is that the function then needs to take into account getting a null value, which is a little annoying. |
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Original comment posted by lowasser@google.com on 2014-07-09 at 04:19 PM In what way? The above implementation (properly) just throws an NPE. |
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Kevin recently said:
I'm closing this and any other |
Original issue created by tomas.zalusky on 2012-10-16 at 02:03 PM
I have an instance which is to be passed through chain of Optional.transform methods. But functions may return null and hence cannot be used in Optional.transform:
Optional.of(obj).transform(function1).transform(function2).orNull();
As Optional provides method fromNullable for construction from null, it could similarly wrap null-returning legacy functions:
class Present
...
@Override public <V> Optional<V> transformToNullable(Function<? super T, V> function) {
V functionResult = function.apply(reference);
return functionResult == null ? Absent.INSTANCE : new Present<V>(functionResult);
}
Until now, following 2 workarounds can be used but first one scales source text badly for long chains and second one is awful abuse of iterables.
V result = null;
V1 result1 = function1.apply(obj);
if (result1 != null) {
result = function2.apply(result1);
}
V result = from(singleton(obj))
.transform(function1).filter(notNull())
.transform(function2).filter(notNull())
.first().orNull();
Thanks!
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