问题
In vanilla Scala the following assertions pass
assert(1D > 0F)
assert(1F > 0)
assert(1L > 0)
assert(1 > 0.toShort)
assert(1.toShort > 0.toChar)
however similar matchers in ScalaTest fail
1D shouldBe > (0F)
1F shouldBe > (0)
1L shouldBe > (0)
1 shouldBe > (0.toShort)
1.toShort shouldBe > (0.toChar)
A workaround is to make both sides the same type, for example
1D shouldBe > (0D)
Why does it work in Scala, but not in Scalatest, or what is it about the signature of >
def >[T : Ordering] (right: T): ResultOfGreaterThanComparison[T]
that makes it fail?
回答1:
Vanilla Scala works due to automatic type conversion i.e. 0F is cast to 0D which is a common practise in many languages.
More interesting question is why shouldBe does not work. De-sugaring the implicits yields
new AnyShouldWrapper[Double](leftSideValue = 1D,
pos = ???,
prettifier = ???)
.shouldBe(new ResultOfGreaterThanComparison[Double](right = 0D))
new AnyShouldWrapper[Double](leftSideValue = 1D,
pos = ???,
prettifier = ???)
.shouldBe(new ResultOfGreaterThanComparison[Float](right = 0F))
which leads to overloaded implementations of shouldBe. The former case goes here and the latter here.
After looking at the source code, it seems that the only reason 1D shouldBe > (0F) actually compiles is to support array comparison with shouldBe keyword.
来源：https://stackoverflow.com/questions/56589516/comparison-matchers-fail-on-mixed-numeric-types