SBT 0.13.8 what does the SettingKey.~= method do

Question

The SettingKey.~= method is used to exclude dependencies from libraryDependencies (see play 2.3.8 sbt excluding logback), but trying to find out what it does is hard as:

There is no documentation about this function at http://www.scala-sbt.org/0.13.12/api/index.html#sbt.SettingKey,
It cannot be searched using Google as it uses symbols in the method name and
Examination of the SBT source code (https://github.com/sbt/sbt/blob/0.13/main/settings/src/main/scala/sbt/Structure.scala#L47) does not provide an obvious answer.

Can anyone shed light on what this does?

"It cannot be searched using Google as it uses symbols in the method name" - just to say that isn't true as I found this question in exactly this way. Maybe Google's gotten a bit smarter about including squiggles in queries. — Nick, Mar 14 '19 at 11:05

score 10 · Answer 1 · answered Jan 13 '17 at 07:32

10

someScopedKey ~= f

is equivalent to

someScopedKey := f(someScopedKey.value)

In other words, it transforms the previous value of the setting/task with a given function. That's literally all there is to know about it.

answered Jan 13 '17 at 07:32

sjrd

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Would I be correct to describe it as a mapping operation? – Woodz Jan 13 '17 at 09:44
I would call it a transformation. It certainly does not follow the (loosely speaking) monadic meaning of `map` as understood in Scala. – sjrd Jan 13 '17 at 12:58
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Hi @sjrd just curious, where was this documented in sbt documentation? – soMuchToLearnAndShare Oct 24 '19 at 13:50

SBT 0.13.8 what does the SettingKey.~= method do

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