Update documentation to clarify Elvis operator semantics #30318
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Updated ternary expression that could be misleading for those unfamiliar with Groovy's Elvis operator semantics. Also added a caution snippet to distinguish the varying interpretations and reinforce the expected behavior in SpEL.
spring-projects-issues
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the
status: waiting-for-triage
sbrannen
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type: documentation
| CAUTION: Beware that the behavior of the Elvis operator follows boolean semantics as opposed | ||
| to object reference semantics. Thus, rather than returning the first operand if it is non-null, | ||
| it returns the first operand if it evaluates to true based on the rules that comprise | ||
| https://groovy-lang.org/semantics.html#the-groovy-truth[The Groovy Truth]. | ||
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That's not entirely true.
SpEL does not honor all of Groovy's "truth" rules.
The SpEL Elvis operator checks for values that are non-null and non-empty (for Strings).
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Thanks @mmanashirov for pointing that subtlety. As @sbrannen has pointed out, the wording in the change is not entirely accurate but the concern is valid. I'll treat it more as a ticket than a PR and will come up with a satisfactory wording in a separate commit, closing this as superseded. No more action required on your part 👍 |
simonbasle
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status: superseded
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Thanks for pointing out that this behavior is specific to Strings. After experiencing a slight burn as a result of this behavior on Strings, I made the false assumption that it consistently behaves according to Groovy's rules for other types as well. You just saved me from another burn in the future! Thank you. |
You're welcome.
I can totally see how you got burned by that: it was an undocumented "feature".
Well, you know what they say about assumptions... I still recall what my 10th grade history teacher told my class about assumptions. Though I don't think it's appropriate to quote that here. 😇 |
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We must have had the same 10th grade history teacher. 😂 |
This commit improves both the javadoc and the reference guide section on the Elvis SpEL operator to clarify that in addition to `null` objects, empty Strings also lead the operator to evaluate to its second operand. The reference guide's advanced snippet is modified to use such an empty String instead of `null` to make that behavior prominent with some code. See spring-projectsgh-30318 Closes spring-projectsgh-30352
This commit improves both the javadoc and the reference guide section on the Elvis SpEL operator to clarify that in addition to `null` objects, empty Strings also lead the operator to evaluate to its second operand. The reference guide's advanced snippet is modified to use such an empty String instead of `null` to make that behavior prominent with some code. See gh-30318 Closes gh-30352
Updated ternary expression that could be misleading for those unfamiliar with Groovy's Elvis operator semantics.
Also added a caution snippet to distinguish the varying interpretations and reinforce the expected behavior in SpEL.