This chapter is from the book
This chapter is from the book
This chapter is from the book
This chapter is from the book
4.2 Accessing Map Values
In Scala, the analogy between functions and maps is particularly close because you use the () notation to look up key values.
scores("Bob")
// Like scores.get("Bob") in Java or scores["Bob"] in JavaScript, Python, or C++
If the map doesn’t contain a value for the requested key, an exception is thrown.
To check whether there is a key with the given value, call the contains method:
if scores.contains("Donald") then scores("Donald") else 0
Since this call combination is so common, there is a shortcut:
scores.getOrElse("Donald", 0)
// If the map contains the key "Bob", return the value; otherwise, return 0.
Finally, the call map.get(key) returns an Option object that is either Some(value for key) or None. We discuss the Option class in Section 4.7, “The Option Type,” on page 56.
NOTE
Given an immutable map, you can turn it into a map with a fixed default value for keys that are not present, or a function to compute such values.
val scores2 = scores.withDefaultValue(0)
scores2("Zelda")
// Yields 0 since "Zelda" is not present
val scores3 = scores.withDefault(_.length)
scores3("Zelda")
// Yields 5, applying the length function to the key that is not present