Scala pattern matching with tuple: matching equal values in the tuple
I have created a function to retrieve a given value from the Pascal Triangle and I've used if statements. Now I want to refactor the function to use pattern matching.
My if based function looks like this:
def valueAt(row: Int, column: Int): Int = {
// ...
else if (row == column) 1 // last column
//
}
My second version of this function, using pattern matching has the following signature:
def valueAt2(row: Int, column: Int): Int = (row, column) match {
// ...
}
Is it possible to define a case for when the row and column have the same value?
I have tried using the same variable name in the case , like this:
case (x, x) => 1 // last column
And I have also tried to use the value of the row in the column, like this:
case (_, row) => 1 // last column
But they don't work. In the first case I have a compilation error and in the second the IDE says that I'm shadowing the variable row from the match .
It this possible?
Thanks.
For the first one, use an if guard:
(1, 2) match { case (x, y) if x == y => 1; ... }
For the second one, when you want to match a variable (instead of binding and shadowing it), you can use backticks (`):
(1, 2) match { case (_, `row`) => 1; ... }
You can use a guard , which is a part of a case expression that can check non-stable conditions, and not surprisingly resembles an if statement:
(row, column) match {
case (x, y) if x == y => 1
// other cases...
}
Note that inputs not matching this guard (ie for which x != y ) would continue to check the other cases, so, for example, another case case (x, y) => ... can follow, and assume x != y .