Use cases for different sbt Key operators
sbt, sbt-native-packager, scala
Solution
You cannot find documentation, because as @JacekLaskowski correctly pointed out all operators except for `+=`, `++=` and `:=` are deprecated.
You can however find the Documentation if you switch to older version of sbt.
If you however are stuck to older version, this is their meaning (via documentation):
- `+=` and `++=` append to previous value, where first appends single element and next appends a `Seq`
- `~=` transforms value, e.g. you want to use value stored in a setting to get a new setting.
- `<<=` depends on another key, for example if you call `organization <<= name`, then `organization` value is equal to `name` value. You can depend on multiple values, e.g. `organization <<= (name, version) { (n, v) => /* do something with values */ }`
- `<+=` and `<++=` are appending with dependencies, like the append, but you can use another's setting value to compute new value
Said that, @JacekLaskowski is right, and if you are using sbt 13.x or greater you should not have to use those operators in favours of macros.
Problem
The documentation for sbt seems to be really lacking here, so I'd like to get a definitive answer on this: what is the difference between "+=", "++=", "<+=", "<++=", and "<<=" when operating on Keys?