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Explaining something for the (largeish N)th time finally awoke me to
the fact that software can explain things. I labored a long time over
this error message: I'm sure it can still use work (and/or it will drive
scalaz users off some kind of cliff) but the simple common case people
have so much trouble with is lit up like a christmas tree and for this I
will take some bullets.
build/pack/bin/scala -e 'class Foo[T] ; Set[Foo[AnyRef]]() + new
Foo[String]' :1: error: type mismatch; found : this.Foo[String]
required: this.Foo[java.lang.Object] Note: String <: java.lang.Object,
but class Foo is invariant in type T. You may wish to define T as +T
instead. (SLS 4.5) class Foo[T] ; Set[Foo[AnyRef]]() + new Foo[String]
^
Review by moors.
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