PartialFunctionValues
Wrapper class that adds a valueAt method to PartialFunction, allowing
you to make statements like:
Wrapper class that adds a valueAt method to PartialFunction, allowing
you to make statements like:
pf.valueAt("VI") should equal (6)
Implicit conversion that adds a valueAt method to PartialFunction.
Implicit conversion that adds a valueAt method to PartialFunction.
the PartialFunction on which to add the valueAt method
Trait that provides an implicit conversion that adds a
valueAtmethod toPartialFunction, which will return the value (result) of the function applied to the argument passed tovalueAt, or throwTestFailedExceptionif the partial function is not defined at the argument.This construct allows you to express in one statement that a partial function should be defined for a particular input, and that its result value should meet some expectation. Here's an example:
pf.valueAt("IV") should equal (4)Or, using an assertion instead of a matcher expression:
assert(pf.valueAt("IV") === 4)Were you to simply invoke
applyon thePartialFunction, passing in an input value, if the partial function wasn't defined at that input, it would throw some exception, but likely not one that provides a stack depth:// Note: a Map[K, V] is a PartialFunction[K, V] val pf: PartialFunction[String, Int] = Map("I" -> 1, "II" -> 2, "III" -> 3, "IV" -> 4) pf("V") should equal (5) // pf("V") throws NoSuchElementExceptionThe
NoSuchElementExceptionthrown in this situation would cause the test to fail, but without providing a stack depth pointing to the failing line of test code. This stack depth, provided byTestFailedException(and a few other ScalaTest exceptions), makes it quicker for users to navigate to the cause of the failure. WithoutPartialFunctionValues, to get a stack depth exception you would need to make two statements, like this:val pf: PartialFunction[String, Int] = Map("I" -> 1, "II" -> 2, "III" -> 3, "IV" -> 4) pf.isDefinedAt("V") should be (true) // throws TestFailedException pf("V") should equal (5)The
PartialFunctionValuestrait allows you to state that more concisely:val pf: PartialFunction[String, Int] = Map("I" -> 1, "II" -> 2, "III" -> 3, "IV" -> 4) pf.valueAt("V") should equal (5) // pf.valueAt("V") throws TestFailedException