PatternMatching
Related Doc:
package stdlib
Same koan as above, but we are pattern matching a list with only one item!
To obtain the second element you can expand on the pattern.
To obtain the second element you can expand on the pattern. Where x is the first element, y is the second element, and xs is the rest:
To pattern match against List, you can also establish a pattern match if you know the exact number of elements in a List:
To pattern match against a List, the list can be split into parts, in this case the head x and the tail xs.
To pattern match against a List, the list can be split into parts, in this case the head x and the tail xs. Since the case doesn't terminate in Nil, xs is interpreted as the rest of the list:
If a pattern is exactly one element longer than a List, it extracts the final Nil:
Pattern matching can match complex expressions:
A backquote can be used to refer to a stable variable in scope to create a case statement - this prevents "variable shadowing":
Scala has a built-in general pattern matching mechanism.
Scala has a built-in general pattern matching mechanism. It allows to match on any sort of data with a first-match policy. Here is a small example which shows how to match against an integer value:
object MatchTest1 extends App { def matchTest(x: Int): String = x match { case 1 => "one" case 2 => "two" case _ => "many" // case _ will trigger if all other cases fail. } println(matchTest(3)) // prints "many" }
The block with the case statements defines a function which maps integers to strings. The match keyword provides a convenient way of applying a function (like the pattern matching function above) to an object.
Scala's pattern matching statement is most useful for matching on algebraic types expressed via case classes.
Scala also allows the definition of patterns independently of case classes, using unapply methods in extractor objects.
Pattern matching returns something:
Pattern matching can return complex values:
A backquote can be used to refer to a method parameter as a stable variable to create a case statement:
Pattern matching can substitute parts of expressions:
Pattern matching can wildcard parts of expressions:
The parameterless execute method has been deprecated and will be removed in a future version of ScalaTest. Please invoke execute with empty parens instead: execute().
The trap method is no longer needed for demos in the REPL, which now abreviates stack traces, and will be removed in a future version of ScalaTest