A disclaimer or two for Optional
brian.goetz at oracle.com
Wed Oct 23 06:48:05 PDT 2013
> Does the paragraph below from Rose's blog list everything that shouldn't
> be done to an Optional?
> A value-safe expression may not be the subject of a value-unsafe
> operation. In particular, it cannot be synchronized on, nor can it
> be compared with the “==” operator, not even with a null or with
> another value-safe type.
Also: System.identityHashCode. And assignment of null.
On the other hand, we are considering whether == and identityHashCode
can be retrofitted to values by an automated componentwise/bitwise
computation. Which means that == is unwise but probably supportable.
The real killer is synchronizing (and its friends, wait/notify.)
> Comparing an Optional with null would be pretty funny. For other
> potential value types, such as Boolean and Integer, comparing with null
> is, unfortunately, a somewhat common idiom: null means "not assigned".
Right. My take is that the existing primitive wrapper types are
hopelessly polluted and must always mean "boxed primitives". But, for
new-in-8 classes (Optional, and the 310 date-time classes), there may be
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