Scala Map: mysterious syntactic sugar?

scala maps syntactic-sugar scala-collections
oxbow_lakes picture oxbow_lakes · Mar 25, 2009 · Viewed 11.7k times · Source

I have just found out this syntax for a scala Map (used here in mutable form)

val m = scala.collection.mutable.Map[String, Int]()
m("Hello") = 5
println(m) //PRINTS Map(Hello -> 5)

Now I'm not sure whether this is syntactic sugar built in to the language, or whether something more fundamental is going on here involving the fact that a map extends a PartialFunction. Could anyone explain?

Answer

starblue picture starblue · Mar 25, 2009

If you mean (it would be nice if you could be more explicit)

m("Hello") = 5

that is intended syntactic sugar for

m.update("Hello", 5)

independent of what m is. This is analogous to

m("Hello")

which is syntactic sugar for

m.apply("Hello")

(I'm just reading "Programming in Scala".)

Related questions

Merge maps by key

Say I have two maps: val a = Map(1 -> "one", 2 -> "two", 3 -> "three") val b = Map(1 -> "un", 2 -> "deux", 3 -> "trois") I want to merge these maps by key, applying some function …

Read More
How to use java.String.format in Scala?

I am trying to use a .format method of a string. But if I place %1, %2, etc. in the string, java.util.UnknownFormatConversionException is thrown pointing to a confusing Java source code piece: private void checkText(String s) { int idx; // If …

Read More
How can I change column types in Spark SQL's DataFrame?

Suppose I'm doing something like: val df = sqlContext.load("com.databricks.spark.csv", Map("path" -> "cars.csv", "header" -> "true")) df.printSchema() root |-- year: string (nullable = true) |-- make: string (nullable = true) |-- model: string (nullable = …

Read More